Genuine Mazda Six-Speed Gearbox Countershaft / Clutch Hub Locking Nut
Replacement Genuine Mazda internal transmission locking nut for Mazda MX-5 Mk3, Mk3.5 and Mk3.75 NC 2.0 Sport models fitted with the factory six-speed manual gearbox.
This nut is installed inside the manual transmission on the countershaft and secures the clutch-hub and associated gear assembly in position. It forms part of the internal shaft assembly rather than the external gearbox mounting or selector mechanism.
Correct retention of the clutch hub and gear stack is essential for maintaining the specified shaft assembly and normal gear engagement. The locking nut should be inspected and renewed when the countershaft is dismantled for gearbox repair.
One locking nut is fitted per applicable six-speed gearbox, and this listing supplies one Genuine Mazda component.
Transmission restriction: This component is for the Mazda six-speed manual transmission. It is not listed for five-speed manual or automatic MX-5 NC gearboxes.
- Part type: Internal gearbox locking nut
- Common names: Countershaft lock nut / clutch-hub locking nut / gearshaft retaining nut
- Mazda catalogue description: Nut, Lock – Clutch Hub
- Installation area: Inside the six-speed manual transmission
- Installation position: Countershaft / clutch-hub assembly
- Function: Retains the clutch hub and associated gear assembly on the transmission shaft
- Transmission application: Six-speed manual
- Quantity fitted per gearbox: 1
- Quantity supplied: 1 locking nut
- Clutch hub included: No
- Countershaft included: No
- Gears or bearings included: No
- Selector fork included: No
- Brand: Genuine Mazda
- Part No.: P601-17-628
- MX-5 fitment: Mk3, Mk3.5 and Mk3.75 NC 2.0 Sport six-speed manual models
Typical reasons for replacement:
- Countershaft dismantled during gearbox rebuilding
- Third/fourth selector-fork or clutch-hub repair
- Original locking nut removed during gear replacement
- Locking feature disturbed during removal
- Nut damaged by staking, unstaking or previous installation
- Threads worn, corroded or cross-threaded
- Drive faces rounded or damaged
- Incorrect non-standard nut previously installed
Quantity advice: One nut is required per six-speed gearbox. This listing supplies one locking nut.
Fitment advice: Confirm that the vehicle is equipped with the factory six-speed manual transmission. Five-speed manual and automatic NC models use different internal transmission arrangements.
Replacement advice: Renew the locking nut whenever removal, staking or the applicable Mazda workshop procedure requires replacement. Do not rely on a previously disturbed locking feature to retain the rebuilt shaft assembly.
Shaft inspection: Inspect the countershaft threads, splines, bearing surfaces and gear-location shoulders before reassembly. A replacement nut will not correct damaged shaft threads or excessive wear elsewhere in the assembly.
Gearbox inspection: Where the transmission is dismantled because of difficult gear selection, jumping out of gear or selector damage, inspect the relevant clutch hub, synchroniser components, selector fork, bearings and gear engagement teeth.
Tightening advice: Install, tighten and secure the nut using the procedure specified for the applicable Mazda six-speed transmission. Correct shaft support, tightening specification and locking method are essential.
Cleanliness advice: Internal gearbox components must be assembled in a clean working environment. Prevent dirt, abrasive material and lint from entering bearings, synchronisers or oil passages.
Other items to inspect: Check the countershaft bearings, clutch hub, synchroniser rings, selector forks, gear teeth, shaft spacers, oil seals and other locking hardware while the gearbox is dismantled.
Useful tools / consumables: Transmission stand or suitable workbench, gearbox pullers and presses, correct sockets, calibrated torque wrench, staking tools where required, circlip pliers, assembly lubricant and the specified manual-transmission oil.
Difficulty guide: DIY Difficulty: Advanced / Specialist. Installation requires removal and dismantling of the manual transmission, accurate shaft assembly and adherence to the Mazda gearbox overhaul procedure.
Why Genuine Mazda? Genuine Mazda transmission hardware matches the original thread, dimensions and locking arrangement used on the six-speed countershaft assembly. Correct internal fasteners are essential for reliable gear and clutch-hub retention.
What’s in the box: One Genuine Mazda countershaft / clutch-hub locking nut, part number P601-17-628.
Installation notes: Remove and dismantle the transmission according to the applicable Mazda workshop procedure. Support the shaft assembly correctly before releasing the original locking nut. Inspect and clean the shaft threads and all adjoining components, then install the replacement nut in the specified orientation. Tighten and secure it using the prescribed procedure before completing shaft and gearbox reassembly. Refill the transmission with the specified oil and check operation before road use.
| Make | Model | Sub Variant | Chassis / Code | Years | Power (PS) | Engine Codes | Fuel | Transmission | Notes |
|---|---|---|---|---|---|---|---|---|---|
| Mazda | MX-5 | Mk3 NC1 – 2.0 Sport | NC18 / NCEC | 2005–2009 | 160 | LF-VE | Petrol | 6-Speed Manual | Internal countershaft / clutch-hub locking nut; one fitted per gearbox; five-speed and automatic gearboxes excluded |
| Mazda | MX-5 | Mk3.5 / Mk3.75 NC2/NC3 – 2.0 Sport | NC18 / NCEC | 2009–2015 | 160 | LF-VE | Petrol | 6-Speed Manual | Internal countershaft / clutch-hub locking nut; one fitted per gearbox; five-speed and automatic gearboxes excluded |
| Vehicle Manufacturer | OEM Reference Number |
|---|---|
| Mazda | P601-17-628 |