{"id":969,"date":"2026-05-22T07:58:08","date_gmt":"2026-05-22T07:58:08","guid":{"rendered":"https:\/\/foragebaler.com\/?p=969"},"modified":"2026-05-22T07:58:08","modified_gmt":"2026-05-22T07:58:08","slug":"round-baler-shear-bolt-slip-clutch-drive-protection","status":"publish","type":"post","link":"https:\/\/foragebaler.com\/hi\/round-baler-shear-bolt-slip-clutch-drive-protection\/","title":{"rendered":"Round Baler Shear Bolts: Selection, Stocking, Drive Protection"},"content":{"rendered":"
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<\/div>\n
Baler Drive Protection Guide<\/span><\/p>\n

Round Baler Shear Bolts: Selection, Stocking, Drive Protection<\/h1>\n

A shear bolt is the least expensive component in the baler \u2014 typically $0.15\u2013$0.60 \u2014 and it is doing its job correctly every time it breaks. It breaks to protect a gearbox that costs $800\u2013$2,500 or a shaft that costs $200\u2013$600. The problem is not when shear bolts break; the problem is when producers install the wrong bolt (too strong, so it never breaks when it should), when they run out of spares mid-field, or when repeated failures at the same location signal a real problem that bolt replacement is masking. This guide covers the shear bolt system completely.<\/p>\n

How the System Works<\/a><\/p>\n<\/div>\n<\/div>\n

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The Shear Bolt System: Designed Failure That Prevents Catastrophic Failure<\/h2>\n

A shear bolt is a fastener calibrated to fracture at a defined torque load \u2014 deliberately the weakest link in the driveline at each protection point. When a rock, wire, or slug of wet crop creates a torque spike that exceeds the shear bolt’s rated strength, the bolt fractures in shear at its reduced-diameter neck, absorbing the overload event and stopping power transmission to the protected component before that component can absorb the destructive force. The shear bolt is sacrificial by design; it is supposed to break.<\/p>\n

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$0.15\u2013$0.60<\/div>\n
Cost of one shear bolt \u2014 the sacrificial component designed to fail instead of a $400\u2013$2,500 gearbox<\/div>\n<\/div>\n
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Never substitute<\/div>\n
Standard grade 5 or grade 8 hardware bolts \u2014 they are too strong and defeat the protection system entirely<\/div>\n<\/div>\n
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Per position<\/div>\n
Each shear bolt location has its own specified size and grade \u2014 do not mix positions or use one-size-fits-all replacements<\/div>\n<\/div>\n<\/div>\n

The shear bolt system has two variants: the single-shear bolt that fractures cleanly and requires manual replacement, and the slip clutch that uses a spring-loaded friction plate to slip (rather than fracture) when overloaded, then re-engage automatically. Many round balers use both \u2014 shear bolts at individual drive points and a slip clutch on the main PTO input shaft. Understanding which protection type is at each location determines the correct service response when an overload event occurs.<\/p>\n<\/div>\n

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Shear Bolt Specification: Why Grade and Diameter Both Matter<\/h2>\n

\"round<\/p>\n

The shear bolt’s trip torque \u2014 the torque load at which it fractures \u2014 is determined by two specification variables: the bolt diameter and the steel grade. A larger diameter or higher grade (stronger steel) raises the trip torque. Both variables must match the manufacturer’s specification for the shear bolt to trip at the correct load. Substituting a bolt with the correct diameter but higher grade (e.g., replacing a Grade 2 with a Grade 5 of the same size) can raise the trip torque by 80\u2013120%, defeating the protection system on that position entirely.<\/p>\n

\n\n\n\n\n\n\n\n
Bolt specification<\/th>\nRelative shear strength<\/th>\nEffect of substituting up one grade<\/th>\n<\/tr>\n<\/thead>\n
Grade 2, 5\/16″ diameter<\/td>\nBaseline (low)<\/td>\nSubstituting Grade 5 same diameter: trip torque rises ~80%. Gearbox no longer protected at design load.<\/td>\n<\/tr>\n
Grade 2, 3\/8″ diameter<\/td>\nMedium-low<\/td>\nCommonly used for medium-duty shear points on pickup drives and secondary shafts<\/td>\n<\/tr>\n
Manufacturer OEM shear bolt<\/td>\nPrecisely calibrated<\/td>\nOEM shear bolts are made from specific alloy at controlled hardness \u2014 not a standard SAE grade bolt. Always prefer OEM for critical protection points.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
Never use standard Grade 5 or Grade 8 hardware bolts as shear bolt substitutes,<\/strong> regardless of how closely they match the shear bolt diameter. Standard hardware bolts are manufactured to minimum strength requirements, not to maximum strength limits \u2014 a Grade 5 bolt may be 40\u201360% stronger than the nominal Grade 5 specification, raising the trip torque far above the design protection point. Use only the specified OEM shear bolt or an aftermarket shear bolt of confirmed equivalent specification.<\/div>\n<\/div>\n
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Locating Every Shear Bolt Position on Your Baler<\/h2>\n

Every round baler has multiple shear bolt positions \u2014 typically 3\u20136 on a mid-range commercial baler. Each position protects a different downstream component, and each position has its own specified bolt. The operator manual lists every shear bolt position with the bolt specification for each. Before the season begins, walk every shear bolt position and confirm the correct bolt is installed, not a hardware store substitute from a prior emergency repair.<\/p>\n

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PTO input shaft shear bolt<\/div>\n

Protects the main gearbox from overload on the primary drive input. This is typically the largest and most precisely calibrated shear bolt on the baler \u2014 any overload large enough to reach the gearbox without being absorbed by a slip clutch must be handled here. On balers without a slip clutch, this bolt is the sole protection for the main gearbox.<\/p>\n<\/div>\n

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Pickup drive shear bolt<\/div>\n

Protects the pickup drum shaft and its drive from rock or wire ingestion. This is the highest-frequency shear bolt failure position on the baler because the pickup is the first component to contact field hazards. The pickup shear bolt is designed to trip at a lower torque than the main drive to ensure pickup hazards don’t transmit to the main driveline.<\/p>\n<\/div>\n

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Auger and feeder shear bolts<\/div>\n

Protect the crop intake augers from slug loads \u2014 a dense, wet wad of crop entering the auger zone can stall the auger if it exceeds the shear bolt’s trip torque. Auger shear bolts are typically smaller diameter and lower grade than pickup bolts because the auger is a lower-torque component.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Slip Clutch Service: The Alternative to Shear Bolts<\/h2>\n

\"round<\/p>\n

A slip clutch protects the driveline by allowing controlled slippage under overload rather than a fracture. When the load exceeds the spring-set friction force, the clutch plates slip against each other \u2014 the drive shaft continues rotating while the driven shaft momentarily stalls \u2014 then re-engage when the torque drops below the slip threshold. The slip clutch has two service requirements: maintaining the correct spring pre-load that sets the slip torque, and keeping the friction plates in a condition that provides consistent friction coefficient.<\/p>\n

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Slip clutch over-torque from tight compression<\/div>\n

A slip clutch that never slips \u2014 even under severe overload conditions \u2014 has its spring pre-load set too tight or has friction plates that are stuck together from corrosion (a common problem after off-season storage). A stuck clutch provides no protection \u2014 it transfers every overload torque spike directly to the gearbox. Test pre-season by operating at idle PTO and briefly blocking the protected shaft by hand (safely) \u2014 a correctly set slip clutch should slip with modest hand force against the shaft.<\/p>\n<\/div>\n

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Slip clutch under-torque from loose spring<\/div>\n

A slip clutch with loose spring compression slips too easily \u2014 tripping during normal operation under crop load rather than only under overload events. This produces the characteristic symptom of intermittent slipping during heavy windrows: the baler slows or stops forwarding crop without a rock or wire cause. Tighten the compression spring to the torque specification in the operator manual. Check spring length against the new-spring specification \u2014 a spring that has taken a permanent set (shorter than nominal) produces lower than specified friction force regardless of adjustment position.<\/p>\n<\/div>\n<\/div>\n

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Annual service<\/div>\n
Disassemble the slip clutch, clean all friction plate surfaces with solvent and dry completely, inspect friction material for glazing or uneven wear, inspect pressure plate for scoring, reassemble with spring pre-load torqued to specification. This prevents the corrosion-bonded clutch failure that is the most common cause of a slip clutch not providing protection.<\/div>\n<\/div>\n
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After severe overload event<\/div>\n
Inspect friction plates for heat discoloration (blue or brown tinting) and check the spring for set compression. An overload severe enough to produce sustained slipping generates heat that can glaze friction surfaces and reduce the friction coefficient, causing the clutch to slip at lower than specified torque afterward. Replace friction plates if glazing is present after any prolonged slipping event.<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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Field Stocking Strategy: How Many Shear Bolts to Carry<\/h2>\n

\"commercial<\/p>\n

Running out of shear bolt spares in the middle of a cutting stops baling entirely until you can drive to a dealer or farm store \u2014 a delay that can cost 2\u20134 hours of prime drying window. The correct field stocking strategy is to carry more shear bolts than you expect to use, organized by position so you grab the right bolt for the right location without searching through a mixed assortment.<\/p>\n

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Recommended Field Spare Kit \u2014 Mid-Size Commercial Round Baler<\/div>\n
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Pickup shear bolts:<\/strong> 12\u201315 spares. These break most frequently \u2014 a rocky field can consume 3\u20135 bolts in a single pass. Keep the most spares of the bolt you will use most.<\/div>\n
PTO \/ main drive shear bolts:<\/strong> 4\u20136 spares. Lower frequency than pickup bolts but critical to have when needed.<\/div>\n
Auger \/ feeder shear bolts:<\/strong> 4\u20136 spares per position. Separate from pickup bolts \u2014 do not mix positions even if diameter appears similar.<\/div>\n<\/div>\n

Store shear bolts in labeled zip-lock bags by position in the tractor cab \u2014 not loose in a toolbox where they mix. The five seconds it takes to grab the labeled bag prevents installing the wrong bolt at the wrong position under field-time pressure.<\/p>\n<\/div>\n

Pre-season consumables inventory \u2014 including shear bolts alongside tines, net wrap knives, and wear items \u2014 with full specification reference is in the round baler parts and wear items guide<\/a>. When shear bolt failures occur repeatedly at the same position, indicating a deeper mechanical issue rather than incidental rock contact, the diagnostic process is in the round baler troubleshooting guide<\/a>. PTO driveline torque specifications and gearbox ratings that define the maximum torque the shear bolt must protect against are in \u0915\u0943\u0937\u093f \u0917\u093f\u092f\u0930\u092c\u0949\u0915\u094d\u0938 \u0914\u0930 \u092a\u0940\u091f\u0940\u0913 \u0921\u094d\u0930\u093e\u0907\u0935\u0932\u093e\u0907\u0928 \u0918\u091f\u0915 \u0935\u093f\u0928\u093f\u0930\u094d\u0926\u0947\u0936<\/a>.<\/p>\n<\/div>\n

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Repeated Shear Bolt Failures: When It’s More Than Bad Luck<\/h2>\n

One or two shear bolt failures per season at a given position is normal incidental overload \u2014 rocks, wire, dense crop slugs. Three or more failures at the same position in the same season, or failures that occur without apparent cause in normal crop conditions, indicate a mechanical problem that is creating chronic overload at that drive point. Continuing to replace bolts without investigating the root cause eventually damages the component the bolt is protecting.<\/p>\n

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Pickup shear bolt failing repeatedly<\/div>\n

Investigate: rock-heavy field (expected \u2014 no action needed beyond stocking more spares); pickup tines bent to angles that cause crop to jam at the tine-to-stripper gap rather than flow through (bent tines create repeated slug loads); stripper fingers worn so wide they allow crop to wrap the pickup drum; or the shear bolt has been replaced with a stronger-than-specified bolt at some prior repair that is only now failing because a normally manageable overload has become repetitive.<\/p>\n<\/div>\n

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PTO \/ main drive shear bolt failing repeatedly<\/div>\n

This is a more serious pattern \u2014 the main drive position should almost never fail except in severe overload events. Repeated main drive shear bolt failures indicate: a bearing failure somewhere in the drive path that creates chronic high resistance (listen for bearing noise before the next bolt is installed); a crop wrap around the main shaft that isn’t visible without inspection; or a significant mismatch between tractor PTO speed and baler specification (baling at 1000 RPM when the baler requires 540 RPM produces approximately 85% over-speed \u2014 dramatically increased torque spikes).<\/p>\n<\/div>\n

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Shear bolts failing with no apparent cause<\/div>\n

If bolts are failing regularly without rock contact or obvious mechanical cause, the most likely explanation is that the replacement bolts are not the correct specification \u2014 either they are understrength (failing too easily under normal crop loads) or there is a genuine mechanical issue that is not yet producing other symptoms. Confirm bolt specification against the operator manual. If specification is correct, inspect the protected component’s bearings, shaft straightness, and mounting hardware for developing problems before the next bolt is installed.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Shear Bolt Replacement Procedure: Getting Back in the Field Safely<\/h2>\n
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SAFETY<\/div>\n

Never replace a shear bolt with the tractor PTO engaged or the engine running. The bolt failed because a mechanical resistance still exists at that drive point \u2014 engaging the PTO with the new bolt installed before clearing the obstruction causes the new bolt to immediately fail or the operator to be injured by sudden rotation of the newly powered component. Always: disengage PTO, turn off engine, clear the obstruction (remove the rock, wire, or crop wrap from the protected drive component), then install the replacement bolt.<\/p>\n<\/div>\n

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1<\/div>\n

Disengage PTO and shut down the engine completely.<\/strong> Wait for all rotation to stop before approaching the failure point.<\/p>\n<\/div>\n

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2<\/div>\n

Identify and remove the obstruction.<\/strong> Look for the rock, wire, or crop wad that caused the failure. If nothing is visible, rotate the failed shaft by hand to feel for resistance \u2014 a bearing failure will produce roughness or catching even without an external obstruction.<\/p>\n<\/div>\n

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3<\/div>\n

Remove both shear bolt halves completely.<\/strong> A common mistake is leaving a remnant of the fractured bolt in the hole \u2014 the next bolt then seats on the remnant at a misaligned angle and fails at a lower torque than designed. Use a punch to drive out any remnant fragment before installing the new bolt.<\/p>\n<\/div>\n

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4<\/div>\n

Install the correct replacement bolt from your labeled spare bag.<\/strong> Thread hand-tight, then tighten to snug (not torqued to specification \u2014 shear bolts are intentionally installed without high preload so the reduced-neck section fractures cleanly in shear).<\/p>\n<\/div>\n

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5<\/div>\n

Rotate the shaft by hand through one full revolution<\/strong> before starting the tractor \u2014 confirms no remaining obstruction and that the shaft turns freely with the new bolt installed.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Shear Bolt and Slip Clutch FAQs<\/h2>\n
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\nMy baler’s shear bolt just broke and I don’t have any spares. What can I do temporarily?+<\/span><\/summary>\n
If the failure is at the pickup position and you have no spares, the temporary option is to bale from a different windrow section while getting correct bolts \u2014 do not attempt to bale with the pickup shear bolt position empty (it will damage the unprotected shaft immediately on the next obstruction). If the failure is at a non-critical secondary position and you have a close-size bolt available, installing a temporary undersized bolt (one size smaller diameter, same grade) allows you to continue baling while accepting that any further overload will cause the temporary bolt to fail more easily than the correct bolt. This is not ideal but is better than installing an oversized bolt. Never install an oversized bolt as a temporary measure \u2014 it removes the overload protection. Get the correct bolts from a dealer as soon as possible and replace the temporary bolt at the end of the day.<\/div>\n<\/details>\n
\nCan I use a shear bolt from one position on the baler at a different position if I run out of the correct size?+<\/span><\/summary>\n
Only if the specifications are identical \u2014 same diameter and same grade. Even a minor difference in diameter (e.g., 5\/16″ vs 3\/8″) produces a significantly different shear strength that may either fail too easily at the stronger position or fail to protect at the weaker position. If you have a secondary position bolt (typically lighter duty) and need to replace a primary position bolt (heavier duty), using the lighter bolt is a temporary measure that accepts higher failure risk \u2014 better than no bolt, but understand the protection is compromised until the correct bolt is installed. If you have a heavier bolt and need to fill a lighter position: do not do this, as it removes protection at that position entirely. Keep each position’s spares clearly labeled and separated to prevent this confusion under field-time pressure.<\/div>\n<\/details>\n
\nHow do I know if my slip clutch is set correctly?+<\/span><\/summary>\n
The definitive test is a torque wrench measurement of the slip torque, but few field operators have access to a high-range torque wrench. A practical field test: with the baler running at the correct PTO speed in normal hay conditions (no rock contact, consistent windrow), the slip clutch should not trip. If it trips during normal baling at normal field speed, the spring is too loose or the friction plates are worn. If the clutch never trips even during clear rock-contact events where you hear the impact, the spring is too tight or the plates are seized. Compare the spring length to the specification in the operator manual as the most accessible diagnostic \u2014 a spring that is compressed shorter than its specification produces higher than intended friction force; a spring at its nominal free length may have taken a set and provides less than intended force. Replace springs at the first sign of set (shorter free length than specification).<\/div>\n<\/details>\n
\nShould I upgrade to a slip clutch baler to eliminate shear bolt interruptions?+<\/span><\/summary>\n
Slip clutches do reduce the production downtime from overload events because they re-engage automatically without a stop-and-replace procedure. In rock-heavy fields where shear bolt replacements are frequent (more than 5\u20138 per cutting day), the productivity benefit of a slip clutch system is real and meaningful. However, slip clutches have their own failure mode \u2014 friction plate wear and seizure \u2014 that requires annual maintenance and eventual friction plate replacement. They also slip repeatedly under any sustained overload condition, generating heat that can glaze the plates and reduce protection quality. The choice between shear bolt and slip clutch systems is fundamentally a management preference: shear bolts require intermittent full-stops for replacement but are simple and low-maintenance; slip clutches allow faster recovery from overloads but require consistent annual service to maintain calibration.<\/div>\n<\/details>\n
\nWhat damage occurs if I operate without a shear bolt installed after one breaks?+<\/span><\/summary>\n
Operating without a shear bolt at a protected position is not the same as operating with the bolt installed and broken. When the bolt is installed and intact, it provides drive transmission through the shear section \u2014 it only fails when torque exceeds the design threshold. When the bolt is absent, the shaft hub is free to rotate within the drive hub without transmitting any torque \u2014 the driven component simply doesn’t receive power, and typically the pickup or auger stops turning. While this is not immediately destructive, it allows the hub bores and key ways to wear against each other without the bolt’s load-bearing support, eventually damaging the hub interfaces. Additionally, operating without understanding which position lost its bolt can lead to crop accumulation and additional damage. The correct action when a bolt fails: stop, identify the failed position, remove the obstruction, install the correct replacement, and only then resume operation.<\/div>\n<\/details>\n
\nWhere is the best source for correct shear bolts at low cost?+<\/span><\/summary>\n
The most reliable source for correctly specified shear bolts is the baler’s OEM parts dealer \u2014 the bolts are sold labeled for their specific position, eliminating any specification ambiguity. OEM shear bolts are more expensive per bolt ($0.60\u2013$2.00 each) but are the safest option for critical positions. Quality aftermarket agricultural parts suppliers (those that specify the bolt by diameter, grade, and application position) provide an acceptable alternative at lower cost \u2014 typically $0.15\u2013$0.50 each in bulk quantities. Avoid hardware store general-purpose bolts entirely, regardless of how closely the diameter matches \u2014 they are not manufactured to the controlled maximum strength ceiling that a shear bolt requires. For bulk stocking, contact your dealer about ordering a season’s supply at the pre-season order and buying in quantities of 25\u201350 per position rather than a few bolts at a time.<\/div>\n<\/details>\n<\/div>\n<\/div>\n
\"foragebaler.com<\/p>\n

Get Shear Bolt Specifications for Every Position on Your Baler<\/h3>\n

Tell us your baler model and which position is experiencing repeated failures. We provide the correct bolt specification for each position and help identify whether the root cause is a mechanical problem rather than incidental field hazards.<\/p>\n

Get Shear Bolt Specifications<\/a><\/p>\n<\/div>\n

\u0938\u0902\u092a\u093e\u0926\u0915: \u0938\u0940\u090f\u0915\u094d\u0938\u090f\u092e<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Baler Drive Protection Guide Round Baler Shear Bolts: Selection, Stocking, Drive Protection A shear bolt is the least expensive component in the baler \u2014 typically $0.15\u2013$0.60 \u2014 and it is doing its job correctly every time it breaks. It breaks to protect a gearbox that costs $800\u2013$2,500 or a shaft that costs $200\u2013$600. The problem […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[28],"tags":[],"class_list":["post-969","post","type-post","status-publish","format-standard","hentry","category-forage-baler"],"_links":{"self":[{"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/posts\/969","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/comments?post=969"}],"version-history":[{"count":2,"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/posts\/969\/revisions"}],"predecessor-version":[{"id":971,"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/posts\/969\/revisions\/971"}],"wp:attachment":[{"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/media?parent=969"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/categories?post=969"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/foragebaler.com\/hi\/wp-json\/wp\/v2\/tags?post=969"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}