oil feed pipe nipple threads?

can anyone tell me what size the threads are in the crankcase for the "oil feed pipe nipple" oem part number 3615-36 used on 36-41 Knuckleheads? this is for the fitting that runs to the vent on the oil tank.

thanks!
-dan

The thread is 1/8 NPT or national pipe thread tapered, a standard US thread for plumbing connections that is in theory self-sealing. Care must be taken to not over-tighten this type thread as the taper can cause cracking in the mating part.
Robbie