If you want to use this part, your car have to update full set parts as below:
8381-121 ------- 8381-108 Gear-18T (2 pcs)/gear-12T (4 pcs)
8381-122 ------- 8381-102 Diff outdrive/pins (dia 2*10mm)
8381-123 ------- 8381-116 Pinion gear outdrive/pins(dia 2*8mm)
8381-124 ------- 8381-112 Assembly of the pinion gear
8381-125 ------- 8381-100 Assembly of diff gear box
8381-126 ------- 8381-101 Diff set
8381-209 ------- 8381-200 Central diff gear box(complete)
8381-210 ------- 8381-201 Central diff set
8381-737 ------- 8381- 735 A dogbone pin
8381-736 ------- 8381-708 wheel axle (2pcs)