Shear Bolt Torque Limiter for PTO Shaft
The Shear Bolt Torque Limiter is a mechanical overload safety device engineered for PTO-driven agricultural machinery. It shields gearboxes, drivelines and implements from costly damage caused by sudden torque spikes or unexpected blockages. When torque exceeds a calibrated threshold, the shear bolt fractures cleanly, instantly disconnecting the drive to prevent catastrophic failure. Core advantages include a low-cost, field-replaceable bolt design, a wide torque range from 570 Nm to 4500 Nm, and compatibility with standard 1 3/8″ Z6 and 1 3/4″ Z6 spline profiles. Ideal for mowers, balers, rotary tillers and grain augers across Australia, this limiter offers dependable, no-fuss protection that keeps your equipment running and your downtime to a minimum.
PTO Shear Bolt Torque Limiter – Reliable Overload Protection for Agricultural Drivelines
The PTO shear bolt torque limiter (also called a shear pin clutch or bolt-type safety clutch) is one of the most trusted and economical overload protection devices in the farming industry. Designed to sit between the PTO shaft and the implement, it uses a sacrificial shear bolt that fractures at a precise torque threshold, instantly disconnecting the drive and saving your gearbox, driveline and implement from expensive damage. GBC (General Bearing Company Pty Ltd.) supplies a comprehensive range of shear bolt torque limiters across Australia, covering torque ratings from 570 Nm right through to 4500 Nm.
Technical Specifications – Shear Bolt Torque Limiter Series
| Series | Torque (Nm) | Spline | A (mm) | B (mm) | C (mm) | D (mm) |
|---|---|---|---|---|---|---|
| 1SB | 570 | 1 3/8"Z6 | 95 | 20 | 35 | M6×40 |
| 1SBT1 | 740 | 45 | M6×40 | |||
| 3SB | 1110 | 1 3/8"Z6 | 102 | 21 | 38 | M8×45 |
| 3SBT1 | 1200 | 40 | M8×45 | |||
| 5SB | 1600 | 1 3/8"Z6 | 114 | 21 | 55 | M8×45 |
| 7SB | 2050 | 1 3/8"Z6 | 152 | 24 | 45 | M10×60 |
| 7SBT1 | 3200 | 1 3/8"Z6 | 152 | 24 | 49 | M12×65 |
| 8SB | 2700 | 1 3/8"Z6 | 152 | 24 | 60 | M12×65 |
| 9SBT1 | 4000 | 1 3/8"Z6 | 152 | 24 | 57 | M12×65 |
| 10SBT1 | 4500 | 1 3/8"Z6 | 152 | 24 | 49 | M14×70 |
Key Features & Benefits
Each shear bolt fractures at a specific torque value, delivering predictable and repeatable overload protection.
Replacement shear bolts are inexpensive and universally available, keeping ongoing maintenance costs minimal.
A broken bolt can be swapped in under five minutes with basic hand tools – no workshop visit needed.
Coverage from 570 Nm to 4500 Nm across multiple series handles everything from light rotary hoes to heavy balers.
Hardened steel hub, precision-machined yoke and quality grease nipple ensure longevity under harsh field conditions.
Standard 1 3/8" Z6 and 1 3/4" Z6 profiles fit the vast majority of PTO shafts used in Australian agriculture.
How a Shear Bolt Torque Limiter Works
Under normal operation the shear bolt holds the hub rigidly to the housing, transmitting torque seamlessly from the PTO shaft to the implement. When a sudden overload occurs – for example a rock entering a slasher, or a baler picking up wire – the torque surges past the bolt’s rated breaking point. The bolt shears, separating the hub from the housing and halting power transfer in milliseconds. The operator stops the tractor, removes the broken bolt halves, inserts a new shear bolt, and resumes work. The entire reset takes only minutes, while the equipment it protects can cost thousands of dollars to repair.
Typical Agricultural Applications
Rocks and hidden debris cause violent torque spikes. The shear bolt breaks before the gearbox does, avoiding major repair bills.
Wire, twine tangles or over-packed bales create peak loads. The limiter disconnects instantly, protecting the baler pickup and rollers.
Blockages from damp grain or foreign objects generate damaging torque. The shear bolt lets the auger stop before the drive bends.
Subsurface roots and rocks create sudden shock loads that threaten the tiller gearbox and blades during soil preparation.
PTO Torque Limiter Type Comparison
| Feature | Shear Bolt | Friction Disc | Ratchet | Automatic (Cam) |
|---|---|---|---|---|
| Torque Range | 570 – 4500 Nm | 800 – 3000 Nm | 400 – 2000 Nm | 1600 – 4500 Nm |
| Reset Method | Replace bolt | Automatic (slips) | Automatic (ratchets) | Automatic (re-engages) |
| Best Application | Infrequent overloads | Frequent slip events | Light-duty, low torque | Heavy-duty, auto-reset |
| Cost | Lowest initial | Moderate | Moderate | Highest |
Installation & Safety Guide
- Switch off the tractor PTO and remove the ignition key before beginning.
- Slide the torque limiter onto the implement input shaft, aligning spline profiles (1 3/8" Z6 or 1 3/4" Z6).
- Secure with the push pin; ensure the grease nipple faces outward.
- Attach the yoke to the PTO shaft using a cross-and-bearing kit.
- Insert the correct shear bolt grade and torque the nut to specification – never substitute with a standard bolt.
- Grease the assembly, engage PTO at low RPM, and verify smooth operation.
⚠ Safety Warning: Always use the correct grade shear bolt supplied by GBC. A higher-grade bolt defeats the limiter’s purpose and risks catastrophic equipment failure.
Selection Guide
Choosing the right shear bolt torque limiter requires matching several parameters:
- Required Torque Rating: Determine the maximum operating torque (Nm). Select a limiter whose bolt breaks above normal running torque but below the implement’s damage threshold.
- PTO Spline Profile: Confirm 1 3/8" Z6 or 1 3/4" Z6.
- PTO Speed: 540 RPM or 1000 RPM.
- Physical Envelope: Check dimensions A, B, C and D against available space.
- Bolt Size: Ensure replacement bolts (M6–M14) are locally available.
Quality Certification & Service
All GBC shear bolt torque limiters are manufactured under ISO 9001:2015 quality management and carry CE marking. Every batch is torque-tested to ±5 % of rated value. GBC backs every sale with a 12-month warranty, fast Australian dispatch and dedicated technical support via sales@australia-drive.com.
Frequently Asked Questions
Can I use a standard bolt instead of the shear bolt?
No. A standard bolt will not fracture at the correct torque and could allow overload to transfer through to your gearbox, causing far more expensive damage.
How often should I replace the shear bolt?
Only after it shears. Carry spares in the field at all times.
My bolt keeps shearing during normal use. What is wrong?
This usually indicates the torque setting is too low or a mechanical issue such as worn bearings. Consider stepping up to a higher-rated series.
Do you ship Australia-wide?
Yes. GBC dispatches to all states and territories, typically within 1–3 business days.
Can I order replacement shear bolts separately?
Absolutely. Available individually or in bulk packs. Contact sales@australia-drive.com.
Customer Reviews
“Running a 6SB on my slasher across 200 acres of rough country. It has saved my gearbox three times this season. Replacement bolts are cheap and always on the tractor.”
“Fitted the 4SBT1 to our rotary hoe. Bolt sheared once on a buried stump – two minutes later we were back at work. Great value.”
“Purchased a 7SBT1 for our cane farm auger. Quality is excellent and delivery to Brisbane was fast.”
“Third season on the 5SB and still going strong. Had to replace the bolt once after hitting a rock with the finishing mower.”
“We run a contract mowing business and these limiters have saved us thousands in gearbox repairs. GBC service in Perth is always helpful.”
Related Products & PTO Accessories
GBC supplies a complete range of PTO shafts and accessories including yokes, safety shields, guard tubes, shaft adapters and universal joints.
Ready to Protect Your Equipment?
Contact GBC today for competitive pricing, expert sizing assistance and fast delivery anywhere in Australia.
Get a Quote
Browse All Products
Email: sales@australia-drive.com
The Shear Bolt Torque Limiter is a mechanical overload safety device engineered for PTO-driven agricultural machinery. It shields gearboxes, drivelines and implements from costly damage caused by sudden torque spikes or unexpected blockages. When torque exceeds a calibrated threshold, the shear bolt fractures cleanly, instantly disconnecting the drive to prevent catastrophic failure. Core advantages include a low-cost, field-replaceable bolt design, a wide torque range from 570 Nm to 4500 Nm, and compatibility with standard 1 3/8″ Z6 and 1 3/4″ Z6 spline profiles. Ideal for mowers, balers, rotary tillers and grain augers across Australia, this limiter offers dependable, no-fuss protection that keeps your equipment running and your downtime to a minimum.
