Genuine Mazda M8 Flanged Nut – 12mm Hex • 99940-0801

Genuine Mazda M8 Flanged Nut – 12mm Hex

Replacement Genuine Mazda M8 flanged nut for Mazda MX-5 Mk1 NA, Mk2/Mk2.5 NB, Mk3/Mk3.5/Mk3.75 NC and Mk4 ND/RF models.

This is a general-purpose Mazda fastener used in numerous engine, body, chassis, trim and ancillary-component locations. The integrated flange spreads the clamping load across a wider surface than a conventional nut and may remove the need for a separate plain washer where Mazda specifies this fastener.

The nut has an M8 thread and a 12mm external hex. One nut is supplied per order quantity.

Application advice: Because 99940-0801 is used in many different locations, compatibility with a vehicle does not confirm that it is correct for every M8 fixing on that vehicle. Compare the original nut, thread pitch, flange diameter and installation position before ordering.

• Part type: Flanged retaining nut
• Common names: Flange nut / integral-washer nut / fixing nut
• Mazda catalogue description: Nut, Flange
• Thread size: M8
• Hex / spanner size: 12mm
• Design: Hexagonal nut with integral flange
• Application: Multiple vehicle locations
• Quantity supplied: 1 nut
• Quantity fitted per vehicle: Varies by installation
• Bolt or stud included: No
• Separate washer included: No
• Brand: Genuine Mazda
• Part No.: 99940-0801

Typical reasons for replacement:

• Original nut missing during dismantling
• Threads damaged or stripped
• Hex rounded during removal
• Nut heavily corroded or seized
• Integral flange distorted or damaged
• Restoration of original Mazda hardware
• Replacement of previously fitted non-standard hardware

Fitment advice: Compare the removed fastener with the product reference and dimensions. Do not identify the nut solely by its 12mm hex size, as Mazda uses different thread diameters, pitches and flange dimensions with similar external hex sizes.

Replacement advice: Inspect the mating bolt or stud before installation. A new nut will not repair damaged, stretched, corroded or cross-threaded male threads.

Other items to consider: Inspect the corresponding bolt or stud, mounting bracket and surrounding components. Replace associated hardware where corrosion or thread damage could prevent the joint from being tightened correctly.

Useful tools / consumables: 12mm socket or spanner, calibrated torque wrench, penetrating fluid, wire brush and suitable thread-cleaning tools.

Difficulty guide: DIY Difficulty: Easy to Advanced depending on the installation position. The fastener itself is straightforward to replace, but access and the importance of the joint vary considerably between applications.

Why Genuine Mazda? Genuine Mazda fasteners match the intended thread specification, flange profile, hex dimensions and material requirements for their catalogue applications. Correct hardware helps maintain the specified clamping force and protects the mating component.

What’s in the box: One Genuine Mazda M8 flanged nut, part number 99940-0801.

Installation notes: Clean and inspect the mating bolt or stud before assembly. Start the nut by hand to prevent cross-threading and ensure the flange seats flat against the mounting surface. Tighten it to the Mazda specification applicable to the exact component and installation position. Do not apply a generic M8 torque value where Mazda specifies a different procedure, locking method or lubricated torque.