Oil Return question

[sl87]

I have a sr20det and was Just wondering what the thread pitch is on this oil return fitting that connects to the block. I've found 1/2" BPST and NPT and not sure if its 16, 18, or 20x1.5. I can't figure it out...lame

http://i27.photobucket.com/albums/c152/sl87/240parts062.jpg
http://i27.photobucket.com/albums/c152/sl87/240parts063.jpg

[godsmack]

take it to a hardware store and match it up with other bolts and see if you can find the right thread.