The Pinion Gear axle hole: 5.0mm/0.196inch, come with 3.175mm coupler to convert the pinions apertures to 3.175mm/0.125inch. Work on 5mm and 3.175mm shaft motors(3660 3670 3674 4274 4268 550 540 3650 etc).
Made of High Quality heavy duty hardened steel, durable.
Novel appearance and exquisite workmanship. Hobbyfire Quality Guarantee- 100% warrenty