THE ACREAGE EQUIPMENT FIELD GUIDE
Shear bolt, slip clutch and overrunning clutch: what is included?
Protection labels describe different jobs in a PTO attachment. A shear-bolt device and a friction slip clutch limit overload in different ways; an overrunning clutch addresses the rotating implement’s inertia as the drive slows. Ask which components are supplied and where they are fitted. One line saying “clutch included” may leave an important part of the package unidentified.
By Acreage Equipment · Reviewed November 7, 2026 · Specification research, not a field test
THE DECISION IN NUMBERS
Worked quote review: one protection label does not answer every question
Model-specific equipment comes from the named manuals and pages. The quote descriptions are hypothetical. Functional definitions come from a component manufacturer and do not establish who made these attachments’ shafts. This is a purchasing-document check, not a replacement or adjustment procedure.
Scroll the table sideways on smaller screens.
| Model and hypothetical quote | Documented configuration | What remains unresolved | Question for the seller |
|---|---|---|---|
| WC68: “shaft with shear protection” | Manual specifies the particular PTO shear bolt | Spare identity and whether spares are included | Which approved part and specification apply to this supplied shaft? |
| FM-54: “overrunning gearbox included” | Internal overrunning gearbox plus shaft slip-clutch pack | The quote identifies only one of the two functions | Does this order include the documented slip-clutch shaft as well? |
| FM-54: “slip-clutch shaft included” | Shaft friction protection and separate gearbox overrun | Clutch condition and applicable setup record | Who verifies the delivered clutch assembly under its manual? |
| FM-54: alternative shaft offered with the same power label | Current manual specifies a slip-clutch package | A power label alone does not establish equivalent protection or geometry | Has WoodMaxx approved the complete replacement configuration? |
Separate overload protection from coast-down
Component maker Bondioli & Pavesi describes a shear-bolt limiter as interrupting power when its bolt shears, and a friction limiter as restricting transmitted torque through controlled relative slip. Its overrunning-clutch description addresses reverse inertial loads during deceleration or stopping. These are functional definitions, not a recommendation to substitute one device for another. The component source does not identify the shaft manufacturer used on the attachments below.
FM-54 documents two different protection components
The current WoodMaxx FM-54 manual identifies a slip-clutch pack on the PTO shaft and an internal overrunning clutch in the gearbox. It describes the gearbox feature as allowing the rotor to coast down when PTO power is disengaged. The product page also lists both. A quote mentioning only an overrunning gearbox has therefore not described the complete supplied shaft package. Ask the seller to identify both components instead of treating the word clutch as one interchangeable accessory.
For a shear-bolt package, the spare must be identified precisely
WC68’s page lists an included shaft with shear protection. Its manual gives a particular bolt diameter, length and strength class. A useful spare-parts quote identifies the manufacturer-approved item for that shaft, rather than an unspecified bag of bolts. Ask whether spares are included and which part record governs reorders. The guide does not establish a stronger replacement as an upgrade or approve a different protection device.
A supplied friction clutch still needs the right service record
FM-54’s manual has a clutch-specific setup section and warns that incorrect spring settings can prevent its intended slippage. The buying question is who supplies the applicable instructions and completes the required setup for the delivered assembly. Do not treat visible clutch hardware as proof that its condition or settings have been checked, especially on a previously used shaft. Keep this service question separate from the shaft-length and guarding assessment.
Compare functions and approved configuration, not the number of labels
Neither a matching horsepower label nor the presence of an extra clutch establishes an approved replacement driveline. Bondioli & Pavesi’s manual ties the driveline, protection devices and guarding to the intended implement. For a proposed change, request implement-manufacturer confirmation of the complete configuration. There is no protection score here: these source descriptions do not rank reliability, predict failures or increase the attachment’s permitted power or material capacity.
Take these questions with you.
- Does the quote identify shaft overload protection and any gearbox overrunning function separately?
- Which exact manual and part record define the supplied shear hardware or friction-clutch assembly and its service requirements?
- If any shaft or protection component differs from the listed package, has the implement manufacturer approved that complete configuration?
Keep these questions with your exact tractor and attachment details.
Use these questions in my seller briefFOLLOW THE NUMBERS
Sources & documentation
Research record reviewed November 7, 2026. Confirm the current manual and the exact revision supplied with your machine.
- Bondioli & Pavesi driveline manual 399USA011/D2 — protection-device functions
- WoodMaxx FM-54 current-model manual — two protection functions and height specification
- WoodMaxx FM-54 official page — slip-clutch shaft, overrunning gearbox, roller and conflicting height
- Woodland Mills WC68 manual Rev C, May 28, 2024 — exact shear-bolt specification
- Woodland Mills WC68 official page — included shaft with shear protection
- Current manual index: FM-54 under Models 2025 to current
