Beskrivning
■ What Is a Shear Bolt Torque Limiter?
A shear bolt torque limiter is a mechanical overload protection device fitted directly onto a PTO drive shaft between the tractor and an implement — such as a mower, baler, tiller, or slurry pump. When the driven implement suddenly encounters an obstruction or mechanical jam, the shear bolt torque limiter reacts almost instantaneously. The shear bolts — precision-engineered to fail at a specific torque threshold — break cleanly, disconnecting the drive train and preventing catastrophic damage to the gearbox, driveline, and the implement itself. It is one of the most cost-effective forms of PTO overload protection available to UK agricultural operators, combining mechanical simplicity with highly repeatable performance across seasons and work cycles.
Unlike friction-based limiters that can slip progressively over time, the shear bolt torque limiter provides a defined, one-time release event. The operator simply replaces the shear bolts — a straightforward field repair requiring only a spanner — and the shaft is back in service. This makes the shear bolt torque limiter exceptionally popular in UK arable farming, silage contracting, and estate groundskeeping, where downtime is costly and simplicity of repair is paramount.
■ Operating Principle & Internal Construction
The shear bolt torque limiter operates on a straightforwardly elegant mechanical principle. Under normal running conditions, the yoke, hub, steel ball, and shear bolt assembly rotate together as a single rigid unit, transmitting torque from the tractor PTO shaft to the implement input. The steel balls are held in engagement by the push pins, and the entire assembly transmits load without slip or energy loss. Once the transmitted torque exceeds the bolt’s rated shear strength — expressed in Newton-metres and determined by the bolt grade and cross-section — the bolt shears cleanly at a precision-milled groove, the hub decouples from the yoke, and the shear bolt torque limiter freewheels freely, dissipating any stored kinetic energy without damaging connected components.
The key internal components include: a forged yoke connected to the PTO tube, a grease nipple for routine lubrication of the bearing interface, precision steel balls that maintain positional engagement under normal load, a splined hub machined to 1 3/8″ Z6 or 1 3/4″ Z6 standards, push pins (supplied in pairs, Qty.=2) that retain the ball detent assembly, and the shear bolt and nut set that defines the release torque. Each component is dimensionally verified to ISO and DIN tolerance standards at the manufacturing stage.
The key internal components include: a forged yoke connected to the PTO tube, a grease nipple for routine lubrication of the bearing interface, precision steel balls that maintain positional engagement under normal load, a splined hub machined to 1 3/8″ Z6 or 1 3/4″ Z6 standards, push pins (supplied in pairs, Qty.=2) that retain the ball detent assembly, and the shear bolt and nut set that defines the release torque. Each component is dimensionally verified to ISO and DIN tolerance standards at the manufacturing stage.
■ Technical Specifications
The shear bolt torque limiter range covers a comprehensive torque spectrum from 570 Nm through to 4500 Nm, accommodating tractors and implements from compact utility machines right through to high-horsepower arable and contracting equipment. All standard series use the 1 3/8″ Z6 or 1 3/4″ Z6 spline profile, fully compatible with tractor PTO standards as used across major UK brands. Dimensional drawings are provided below for installer and OEM reference.
Series 1SB – 7SBT1 (Spline: 1 3/8″ Z6)
Series 7NSB – 42SBT1.C (Extended Range)
■ Materials, Build Quality & Application Scenarios
The yoke bodies are manufactured from drop-forged steel with a protective surface treatment that resists the corrosive conditions common to UK outdoor agricultural use — mud, fertiliser spray, moisture and UV exposure throughout the full working year. The hub is precision-machined from medium-carbon steel and case-hardened at the spline engagement zone to maximise wear life across thousands of PTO engagement cycles. Shear bolts are supplied in matched-grade sets, and the steel balls within the detent mechanism are ground to a tight tolerance to ensure consistent, repeatable release at the rated torque point.
The shear bolt torque limiter finds application across an exceptionally broad range of UK farm machinery and groundskeeping equipment. Flail mowers and rotary cutters mounted on compact tractors benefit enormously from units in the 570–1200 Nm range, where strikes against hidden rocks, fence posts or tree stumps are frequent and the cost of gearbox damage is high. Straw choppers, slurry injectors, seed drills, and bale wrappers used by UK contracting firms and larger arable operations will typically specify mid-range units in the 1400–2500 Nm bracket, where the implement input shafts are heavier and the power being transmitted from 80–150 hp tractors is substantially greater. High-capacity disc mowers, large-format round balers, and commercial turf-care machinery operating on golf courses and motorsport venues across England and Scotland will often require the upper-range 3500–4500 Nm series.
■ Why UK Buyers Choose Our Shear Bolt Torque Limiter
■ Complete PTO Drive Shaft Range
The shear bolt torque limiter is designed to integrate seamlessly with our full programme of PTO drive shafts, which are manufactured to cover the complete range of UK tractor and implement combinations from compact horticultural tractors through to high-horsepower row-crop machines. Each series is engineered to specific torque and length envelopes, with options including welded tubes, telescopic profiles, and integrated CE-compliant guarding.
■ Factory & Custom Manufacturing Capability
Our manufacturing facility operates CNC machining centres, precision forging lines, and automated quality control inspection systems across a multi-shift production programme. The shear bolt torque limiter range is produced under rigorous process controls, with dimensional verification conducted at multiple stages from raw material receipt through to final assembly and pre-despatch testing. We hold extensive stock across all standard series, supporting short lead times for UK farm machinery dealers, wholesalers, and independent repair workshops.
Product customisation is a core capability at our factory. We regularly engineer bespoke shear bolt torque limiter variants to customer specification — adjusted torque release values, alternative spline profiles, non-standard bolt diameters, specialist corrosion-resistant surface treatments, and custom-branded packaging for implement OEMs. If your application falls outside the standard range, our engineering team will work with your technical team to develop a solution that meets your requirements. Minimum order quantities for custom variants are competitive and we can supply print-ready documentation including CE declarations for integration into your own implement technical files. Contact us for a detailed quotation on your specific requirements.
■ Customer Success & Application Stories
Our shear bolt torque limiter units are supplied to farm machinery dealers, agricultural wholesalers, and direct OEM customers across the United Kingdom and Ireland. The following case represents a typical application solved with our product range.
Lincolnshire Contracting Business — Flail Mower Gearbox Damage
Utmaning: A 12-tractor arable and grass contracting operation based near Lincoln was experiencing recurring gearbox failures on their fleet of heavy-duty flail mowers used for roadside grass cutting and hedgerow management contracts. Strikes against concealed debris — stones, metal posts, old fencing wire — were destroying gearboxes at a cost of £800–£1,200 per replacement, with downtime during the peak summer cutting season proving particularly disruptive to contract commitments.
Solution & Outcome: Following a recommendation from their local agricultural merchant, the business retrofitted our 5SBT1 shear bolt torque limiter units (2100 Nm) to all eight of their flail mower drivelines. Over the following two seasons, gearbox replacement costs dropped to zero on protected units. Shear bolt replacement events occurred an average of four times per machine per season — a consumable cost of under £15 per event compared with the previous gearbox replacement expenditure. The business has since standardised on our torque limiter range across their entire implement fleet and now sources replacement bolt kits directly through us on a standing order arrangement.
We’ve been using these torque limiters on our round baler fleet for three seasons now. Shear bolt releases are quick to reset in the field and we haven’t had a driveline failure since fitting them. Solid quality at a very fair price point for the volume we buy.
Ordered a batch of 5SB and 7SB units for a power harrow application on our Scottish estate. Delivery was fast, the specs matched the drawings exactly, and the customer service team were very helpful when we needed to confirm the bolt grade. Will definitely order again.
We supply these to our customers as a standard fitment recommendation whenever they buy a mower or tiller PTO shaft from us. The 9SBT1 series has been particularly popular for our larger baler customers. Reliable product, competitive pricing, and the lead times are very manageable.
■ Vanliga frågor
Common questions from UK agricultural buyers, farm machinery dealers, and contracting firms about the shear bolt torque limiter.
Ready to Order or Request a Quotation?
Contact our sales team for pricing, series selection guidance, and custom OEM enquiries. We supply shear bolt torque limiter units to UK agricultural dealers, merchants, and direct buyers.
