Arrma 4x4 Differential Planetary Gear Set.  
Fits:
BIGROCK BLX 4X4 #ARA102723  #AR102711
GRANITE MEGA 4X4 #ARA102714T1 #ARA102714T2 
GRANITE BLX 4X4  #ARA102720T1 #ARA102720T2 #AR102666
KRATON BLX 4X4 #ARA102690 #ARA102692
SENTON MEGA 4X4 #ARA102715T1 #ARA102715T2
SENTON BLX 4X4 #ARA102721T1 #ARA102721T2 #AR102668
TYPHON MEGA 4X4 #ARA102694 
TYPHON BLX 4X4 #ARA102722 #AR102696
GRANITE MEGA 4X4 #AR102665 #AR102676
SENTON MEGA 4X4 #AR102667 #AR102678