Info needed: Transfer case vent

[Jacques Reed]

Originally Posted by Grant Bowker

Based only on the part being designed/made in Canada my assumption is that it would be NPT (North American specification). This needs confirmation.

I am with NPT also but haven't got those thread gauges to compare on my fittings. There are a few British threads on CMP vehicle so you cannot completely write off BSP- Wheel studs at 7/8" BSF are a good example.

NPT thread taper is 1:16, ¾” per foot- from Machinery’s handbook
BSPT is 1°47’ per side equals Sin 0.0311 = 1/ Sin1°47’= 1/32 each side = 1/16 (same as NPT!)

1/8 NPT 27 TPI 1/8 BSP 28 TPI
¼ NPT 18 TPI ¼ BSP 19 TPI
½ NPT 14 TPI ½ BSP 14 TPI

1/2" NPT vs 1/2" BSP: Both have 14 threads per inch, so they match up quite well. The primary difference is angle of the thread which is 60 degrees NPT to 55 degrees BSP. In low pressure applications they are ok to swap. Add PTFE tape as a bit of insurance if you feel it needs it.

In Australia NPT fittings are very hard to find. I was looking for a short 1/2" NPT nipple for the same location to swap different types of breather caps. Could get a s/s one from Canada from a home brewing company but the cost was excessive so left things as is. Shown is one available. No hexagonal area in the middle and very short like the original nipple on the transfer case.

Cheers,