Correct gear to adapt your 2mm shaft motor (like many 20mm inrunners) into our 3.8:1 planetary gearbox. Width .199" (5mm). 15 tooth. Modulus/pitch is unknown. It's finer than .6mod and coarser than .3mod. Might be an engliish gear? Proper sun gear for the RRC 3.8:1 planetary gearbox.