-6an for transmission lines?

Yes, the holes in the transmission are 1/8 NPS (National Pipe Straight). There are special fittings made for this (but you can usually get away with regular NPT fittings, since these are very low pressure. But the threads in the transmission can be damaged by using NPT fittings.):
Fragola Performance Systems Transmission Line Adapter Fittings 481671-BL

What is the difference between NPT and NPS thread? | US Plastic Corporation