H60139AT One-way Bearing Shaft.
Use with 180T M0.6 Autorotation Tail Drive Gear(H60020A):

* Must with Torque Tube Front Drive Gear Set (H60121) or (H60147) or (H60122) .Suitable use for T-REX 600E/600N/550E
Use with 131T M0.8 Autorotation Tail Drive Gear(H60198):

* Must with Torque Tube Front Drive Gear Set (H60228) or (H60229).Suitable use for T-REX 550E upgrade(suggestion)