I did some searching and I found that it was suppose to be a 3/4x16 thread size, so I thread a piece on with those specs and notta. Looking for some absolute clarification.

They changed to the 3/4-16 on the 95 and newer motors. The 91-94 motors were metric. I don't recall the size right now though. Sorry.

20mm x 1.5 thread

I thought that the lowports were metric?

I thought that the lowports were metric?all b13 sr20's have the same thread

they are both the same, just the equivalent size from metric to imperial

they are both the same, just the equivalent size from metric to imperial3/4-16 is not 20mm-1.5

sorry mis-interpreted the following article, ppl use them interchangeably
http://websorcerer.com/GeekOut/index.html

Some have sucess w/ interchangeability some have not. I was one of the unlucky ones that used a B14 oem filter on a 94 B13 that was the 1st year lowport, had 3/4- 16 threads oem. Loud pop @ 70mph w/ 0 compresion, oil everywhere on the highway, under the hood...... filter was installed properly, 1/4 turn past snug. IMHO the thread pattern of 95+ SRs is "definitely different" from earlier SRs even though they are interchangeable to others who have done it. 95+ SRs are definitely metric......