The OS Engines GT15HZ600- 50 class engine is for electric 600 helicopters. GT15HZ600 is equipped with original designed carburetor and bump system. With same crankshaft thread from 50SX and 55HZ, GT15HZ600 can be equipped with compatible fan and clutch. O.S. Engine is releasing upgrade parts for T-REX 600N. With same crankshaft thread from 50SX and 55HZ, GT15HZ600 is compatible with 50 class fan and clutch.