Info needed: Transfer case vent

[Jacques Reed]

Originally Posted by Jacques Reed

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,

Good Day,

Today I thought I would gamble $3.00 on a 1/2 BSP short nipple for my transfer case vent. A local home brewing supplier had these nipples. Although they told me on the phone that they had the straight ones without the hex in the middle when I got there that type was out of stock and they were not reordering them. Not an uncommon thing when chasing up parts.

I prefer the large breather cap to the smaller one so this will do in the interim. I can wait until I get the original style nipple- most likely from China on EPay. I still think the threads on the transfer case are NPT and if so, this proves that 1/2 BSP will do the job if 1/2 NPT isn't available, at least in low pressure applications.

Cheers,