Technical Thread ID - Transdapt Remote Oil Cooler

I'm sorting out oil pressure gauge/switch fittings into a Transdapt remote oil filter like the one below.

I need to know the thread for the oil lines going/out. Local shops don't have any experience of American threads and identified the thread on my Stewart Warner oil pressure sender as M10 fine!!

 

Looks like 3/8 pipe thread to me.

 

Should be American National Standard Pipe Thread. So 3/8" would be known as 3/8-NPT. They are a tapered thread. Go online and you can find a size chart to determine your size. The 3/8" is most common, but some were 1/2".