This is among the most expensive TT-01 upgrade but it is very extremely worthy for serious TT-01D drifters. TAMIYA produced this one way using very high quality materials and part. The instruction manual is straight forward and easy to understand. I assembled the front one-way unit and installed it into my TT-01D. Guess what, this one-way unit really makes my TT-01D totally a different car in terms of car handling characteristics. My TT-01D can make sharp turn on the tight carpet and cement track while tapping the brake just a little. The front one-way comes with a pair of steel joint cup that supports stock TT-01 drive shaft (plastic dog bones). Note that I am still using stock TT-01 drive shaft all around and not upgraded to universal shaft, yet my TT-01D still drifts very well. TAMIYA Front One-Way Unit For TT01 is not like other brands produce front one-way for TT-01 with small joint cup which required to expense more for the universal shaft. Nothing beats the original TAMIYA hop-up option parts.