I ordered an electric tranny temperature guage. I would like to install the sending unit in the line going to the cooler. It looks like the best place to connect is right where the cooler line exits the transmission. There is a union (nipple) coming out of the transmission that connects to the tranny line with a flare fitting. I would like to install a tee in the line. The sending unit is 1/8" with a 3/8" adaptor with NPT threads. I'm pretty sure the tranny lines are 3/8". Does anyone know what the thread type is on the union that goes into the tranny? I thought about removing the union, getting a 3/8" street tee (1 male, 2 female ends) that could thread into the tranny, installing the sending unit in one section of the tee, then putting the union into the other female end of the tee and connecting the tranny line. If I can't find a street tee, I'll need to get a hex nipple to go into the tranny then use a regular tee.

I know there are several different thread types when you get into brass fittings, and I wanted to make sure I picked up the right fittings. I was hoping the pick up the parts and do the job quickly, rather than taking the lines apart and loosing tranny fluid while I run to the hardware store. If anyone has pictures or better ideas on how to make the connections I would appreciate it. Thanks.