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What Is the RA Overrunning Clutch?
The RA Overrunning Clutch is a purpose-built mechanical component that sits at the heart of modern PTO drive shaft assemblies. Designed to transmit torque in a single rotational direction while allowing the driven shaft to rotate freely when the input slows or stops, the RA Overrunning Clutch effectively prevents reverse torque transmission — a critical safety and performance requirement in UK agricultural and industrial machinery. Whether you are running a flail mower across Yorkshire farmland, operating a rotary slasher in Scotland, or driving a heavy-duty spreader in the East Midlands, this clutch delivers the protection your equipment demands.
At pto-drive-shafts.com, the RA Overrunning Clutch is supplied as a premium-grade component machined from high-strength alloy steel, surface-hardened for wear resistance, and engineered to integrate seamlessly with 1 3/8″ Z6 spline configurations. Available across a full range of series variants — from 1RA1 through 8RA2 — this component accommodates maximum torque ratings of 2400 Nm and 3500 Nm respectively, making it suitable for everything from lightweight tractor implements to high-demand commercial agricultural machinery.
The design philosophy behind the RA Overrunning Clutch prioritises reliability under cyclical loading. Unlike simpler friction-based devices, the prong-and-hub mechanism employed in this clutch provides consistent engagement and disengagement across thousands of operating cycles without perceptible performance degradation. For machinery operators and procurement managers across the United Kingdom, this translates directly into reduced downtime, lower maintenance overhead, and a measurably longer service life for the entire drivetrain assembly.
Product Advantages
Automatic Torque Disengagement
Instantly releases reverse torque to protect gearboxes, universal joints, and implement drivelines from shock loading.
Heavy-Duty Alloy Construction
Forged and machined from high-grade alloy steel with surface hardening treatment, delivering outstanding resistance to fatigue and wear.
Wide Torque Range
Two torque ratings — 2400 Nm (RA1 series) and 3500 Nm (RA2 series) — cover the full spectrum of UK tractor and implement requirements.
Standard Spline Compatibility
1 3/8″ Z6 spline interface ensures direct compatibility with the vast majority of agricultural tractors and implements used across the UK.
Grease Nipple for Easy Servicing
Integrated grease nipple on the housing permits on-farm lubrication without disassembly — keeping your machinery moving during critical harvesting seasons.
Custom Configuration Available
Non-standard bore sizes, special surface coatings, and OEM-specific configurations available upon request from our engineering team.
Working Principle, Materials & Application Scenarios
The RA Overrunning Clutch operates on the principle of one-way mechanical engagement via a precision-machined prong-and-hub mechanism. When the input shaft (connected to the tractor PTO) rotates in the drive direction, the three prong kits lock against the hub, transmitting full torque to the implement. The moment the tractor PTO decelerates or stops — whether due to engine braking, disengagement, or sudden tractor deceleration — the hub and prongs release, allowing the implement’s inertia mass (such as a heavy rotor or flywheel) to continue spinning freely without feeding destructive reverse torque back into the drivetrain. This elegant mechanical logic eliminates the need for electronics or hydraulic intervention while providing near-instantaneous response.
In terms of materials, the housing with yoke and the hub are precision-forged from medium-carbon alloy steel, subsequently heat-treated to achieve surface hardness in the HRC 58–62 range. The prong kits — supplied as a set of three per unit — are manufactured from case-hardened spring steel, providing both flexibility for engagement and hardness for long-term wear resistance. The circlip and retaining washer are manufactured from SAE 1070 spring steel, while the push pin kit uses a precision-ground tool steel to maintain consistent engagement force over the product’s service life.
Typical application scenarios for the RA Overrunning Clutch within the UK market include flail mowers, rotary cutters, slurry spreaders, power harrows, round balers, and silage choppers. For agricultural contractors in counties such as Lincolnshire, Norfolk, and Devon — where machinery operates across extended seasonal schedules — the RA clutch provides the protection necessary to maintain drivetrain integrity across repeated daily engagement cycles. Industrial users in conveyor drive systems, crop processing lines, and packaging machinery have similarly found value in the RA series for its mechanical simplicity and low maintenance profile. 
Component Parts List
| No. | Keterangan | Catatan |
|---|---|---|
| 1 | Circlip | |
| 2 | Retaining washer | |
| 3 | Push pin kit | |
| 4 | Hub | |
| 5 | Prong kit | Qty. = 3 |
| 6 | Housing with yoke | |
| 7 | Grease nipple |
Technical Specifications
RA1 Series — Max Torque: 2400 Nm | Spline: 1 3/8″ Z6 | B = 21 mm
| Seri | Max Torque (Nm) | Spline | A (mm) | B (mm) |
|---|---|---|---|---|
| 1RA1 | 2400 | 1 3/8″ Z6 | 138 | 21 |
| 2RA1 | 2400 | 1 3/8″ Z6 | 138 | 21 |
| 3RA1 | 2400 | 1 3/8″ Z6 | 149 | 21 |
| 4RA1 | 2400 | 1 3/8″ Z6 | 150 | 21 |
| 5RA1 | 2400 | 1 3/8″ Z6 | 154 | 21 |
| 6RA1 | 2400 | 1 3/8″ Z6 | 160 | 21 |
| 7RA1 | 2400 | 1 3/8″ Z6 | 171 | 21 |
| 7NRA1 | 2400 | 1 3/8″ Z6 | 157 | 21 |
| 8RA1 | 2400 | 1 3/8″ Z6 | 171 | 21 |
RA2 Series — Max Torque: 3500 Nm | Spline: 1 3/8″ Z6 | B = 21 mm
| Seri | Max Torque (Nm) | Spline | A (mm) | B (mm) |
|---|---|---|---|---|
| 5RA2 | 3500 | 1 3/8″ Z6 | 172 | 21 |
| 6RA2 | 3500 | 1 3/8″ Z6 | 178 | 21 |
| 7NRA2 | 3500 | 1 3/8″ Z6 | 175 | 21 |
| 6RA2 | 3500 | 1 3/8″ Z6 | 178 | 21 |
| 8RA2 | 3500 | 1 3/8″ Z6 | 189 | 21 |
Complete PTO Drive Shaft Range
The RA Overrunning Clutch is designed to integrate with our full range of PTO drive shafts, each optimised for different torque and application requirements across UK agriculture and industry. Whether you need a compact light-duty assembly or a heavy-duty telescopic shaft for high-power tractors, our engineering team can match the right shaft series to your specific implement and operating conditions.
PTO Drive Shaft G Series
A versatile general-purpose PTO shaft suitable for medium-duty implements including mowers, spreaders, and tillers. Ideal for everyday farm use across the UK.
PTO Drive Shaft S Series
Designed for demanding seasonal applications, the S Series PTO drive shaft delivers enhanced durability and torque capacity for heavy implement use on British farms.
PTO Drive Shaft L Series
The L Series offers extended length options and high articulation angles, making it the preferred choice for compact tractors and offset implement mounting.
PTO Drive Shaft T Series
The T Series is built for high-torque transmission in professional agricultural contracting, large-acreage operations, and power-intensive implement combinations.
Customer Success Case
Hargreaves Agricultural Contracting, based in Lincolnshire, approached us in spring 2024 after experiencing repeated drivetrain failures on their fleet of six-metre flail mowers. Operating across heavy clay soils, their machinery was regularly subjected to sudden rotor deceleration events when encountering embedded stones and root masses. Within a single season, they had experienced two gearbox failures and three universal joint replacements — all attributable to reverse torque spikes passing through the shaft assembly.
Following a technical consultation with our engineering team, Hargreaves retrofitted the 6RA1 Overrunning Clutch across their entire mower fleet. Over the following twelve months, they reported zero gearbox failures, a 68% reduction in driveline component replacement costs, and a marked improvement in driver confidence during operation in difficult conditions. The retrofit paid for itself within the first cutting season, and Hargreaves subsequently ordered RA clutch assemblies for their round baler and power harrow fleet as well.
We have been specifying RA clutches on all new shaft orders for three seasons now. The reduction in drivetrain repairs during harvest has been significant — our maintenance costs are down and our operators are far happier. Delivery from pto-drive-shafts.com was straightforward and the technical support was excellent.
James Hargreaves
Director, Hargreaves Agricultural Contracting — Lincolnshire, UK
We source overrunning clutch assemblies for our rotary cutter repair and refurbishment workshop. The RA series from pto-drive-shafts.com matches up perfectly to the OEM dimensions we work with, and the build quality holds up well under sustained commercial use. Competitive pricing and fast despatch to Yorkshire.
David Thornton
Workshop Manager, Thornton Farm Machinery — North Yorkshire, UK
I manage procurement for a Scottish arable farming operation running twelve tractors across spring barley and oilseed rape. The 5RA2 clutches we fitted to our power harrow shafts last spring have been completely trouble-free across two full seasons. Highly recommend contacting the team for bulk pricing.
Fiona MacAllister
Operations Manager, MacAllister Arable Ltd — Aberdeenshire, Scotland
Manufacturing Facility & Custom Product Capability
Our manufacturing facility operates a full complement of CNC turning centres, gear hobbing machines, and surface treatment lines dedicated to PTO drivetrain components. Every RA Overrunning Clutch is produced from controlled raw material batches, with dimensional verification at each production stage and final torque testing prior to despatch. Our quality management system is built to ISO 9001 standards, and our production capacity supports both standard off-the-shelf orders and high-volume scheduled supply agreements with UK agricultural machinery distributors.
Custom product development is a core capability at pto-drive-shafts.com. We regularly undertake projects for UK OEM manufacturers requiring non-standard bore configurations, modified housing dimensions, alternative surface treatments, or special assembly configurations to suit proprietary implement designs. Our engineering team works directly with your technical staff to review drawings, confirm tolerances, and agree on inspection criteria before production begins. Small-batch prototype runs are available with lead times from 20 working days, scaling to full production quantities once design approval is confirmed.
Pertanyaan yang Sering Diajukan
What is the price of an RA Overrunning Clutch for agricultural PTO shafts in the UK, and how can I get a quote?
Pricing for the RA Overrunning Clutch varies by series and quantity. We supply both single units and bulk orders to UK agricultural machinery dealers, repair workshops, and farm operations. To get an accurate price and lead time, email your series requirement and quantity to [email protected] and our sales team will respond promptly with a full quote.
Which RA Overrunning Clutch series should I choose for a UK flail mower or rotary cutter running on a 100 hp tractor?
For a flail mower or rotary cutter attached to a tractor in the 80–120 hp range, we typically recommend the 5RA1 or 6RA1 for standard duty, or the 5RA2 if peak torque loads are expected to approach or exceed 2400 Nm. Please provide your tractor PTO output, implement mass, and operating conditions when contacting us, and we can confirm the correct series for your application.
How does an RA Overrunning Clutch work, and why do I need one on my PTO drive shaft?
The RA Overrunning Clutch allows torque to pass in the drive direction only. When the PTO input decelerates, the internal prong mechanism releases, letting the implement’s rotating mass spin freely rather than feeding reverse torque back through the gearbox and universal joints. This mechanical protection prevents shock loads, extending the service life of your entire drivetrain and reducing unplanned repair costs.
Where can I find a reliable RA Overrunning Clutch supplier in the UK for agricultural machinery repair?
pto-drive-shafts.com supplies RA Overrunning Clutches to agricultural machinery workshops, dealers, and farm operations throughout England, Scotland, and Wales. Our online ordering and direct email quoting process makes it straightforward to source the right component quickly, with competitive pricing and technical support from our engineering team included.
What is the maximum torque rating of the RA Overrunning Clutch, and which series handles the highest loads?
The RA1 series handles a maximum of 2400 Nm, covering the majority of standard agricultural implement applications. The RA2 series is rated to 3500 Nm, suited to large implements, high-power tractor applications, and commercial contracting machinery where sustained high-torque operation is expected.
Can I order a custom RA Overrunning Clutch with non-standard bore dimensions for an OEM implement design?
Yes. Our factory supports custom clutch configurations including modified bore sizes, alternative housing geometries, and specialist surface treatments. OEM enquiries are handled directly by our engineering team. Send your drawings or specification requirements to [email protected] to begin a custom product discussion.
When should I replace the prong kit on my RA Overrunning Clutch, and how difficult is it to service?
Prong kits (Qty. = 3 per unit) should be inspected at the start and end of each working season and replaced if there is visible wear on the engagement faces or if the clutch begins to slip inconsistently. Servicing is straightforward — the circlip and retaining washer are removable with standard agricultural workshop tools, and replacement prong kits are available directly from us. Regular greasing via the integrated nipple extends intervals considerably.
Ready to Order or Need Technical Advice?
Our engineering team is based at the factory and available to answer UK supplier enquiries, specification questions, and custom development requests.
✉ Get a Quote — [email protected]
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