1/8-27 NPT or just 1/8NPT is the size for the plug on the side of the trans, so if the temp probe itself is small enough diameter wise, you can get a whatever size to 1/8NPT female adapter with a male 1/8NPT on the other end and do it that way.
Aslong as you plumb it good, you shouldn't have any leaks with the extra fittings.
Im thinking Stewart Warner might have something like a 1/4NPT or 3/8NPT for their temp senders thread size, most (Autometer, Isspro, etc.) seem to often use 1/8NPT for the temp senders.
Here's some dry read for tapered pipe threads,
pipe threads
Last edited by Lord Tauk : 09-29-2007 at 08:06 AM.