TAMIYA pinion gear set are subject to wear and tear due to prolong usage. Previously I am using TAMIYA TT-01D with stock gearing 19T pinion and 61T spur and now the pinion had worn out. I buy this TAMIYA (#50356) 20T, 21T AV Pinion Gear Set from RCMART and using 20T now. My TT-01D drifts well on the carpet track and surprisingly silent. I recommend this set because if you buy the 18T, 19T AV Pinion Gear Set, you only have to use the 19T pinion and left 18T unused. Meanwhile both 20T and 21T AV Pinion Gear still can match with stock 61T spur gear. Thanks RCMART for the reasonable price.