GPM Racing 40CR Steel Motor Gear 21T (Module:0.5mm,motor Tooth Diameter:3.175mm) (MG321T/0.5M)

Precision small pinion overview

This GPM MG321T/0.5M motor gear is a compact pinion aimed at scale RC drivetrains that require a 21-tooth, 0.5mm module pinion. The item is made from 40Cr steel with a hardened black surface finish to provide improved durability compared with non-hardened replacements.

Primary dimensions are listed so you can confirm fitment: 21T tooth count, 0.5mm module, and motor tooth diameter 3.175mm with a round motor bore. The pinion fastens to the motor shaft with two 3x3 set screws; check shaft style and pinion spacing prior to installation for correct mesh.

For typical replacement and modest tuning the pinion keeps mesh geometry predictable, the hardened steel resists premature wear in normal RC loading, and the round bore with dual set screws simplifies alignment on common motor shafts. Confirm mesh clearance after fitting and before operation.

Can I use this on any round motor shaft?

It fits motors with round shafts that accept set-screw pinions, but you must confirm the shaft diameter and ensure there is adequate shaft length for two 3x3 set screws to clamp securely.

How does the material choice help longevity?

40Cr steel with a hardened surface improves resistance to abrasion and deformation compared with untreated materials, which helps the pinion endure longer under standard RC use.

What checks should I perform after fitting?

After installing, verify correct tooth engagement by hand-rotating the drivetrain, inspect for smooth contact across the tooth face, and retighten set screws if any movement is detected. Write Product Review Please sign in your account before you can write any review. Sign In Close

Made to order: GPM Racing parts are shipped to us from GPM's factory, so please allow around 14 days for dispatch.