NPT 1/8 x 27: dies vary in diameter

Well this thing thickens. I belong to another forum and have been told there that the block thread is BPT. An owner gave me a source which sells a T brass fitting with male 1/8 BPT to block and two females, one 27 and one 28. These guys should know. Still dangling evidence: The sensor removed has "27" stamped on it. My comparisons of thread mesh to one another and to two different thread gauges could be off with tired old eyes. Why would the mighty Japanese auto industry adapt a BPT? The adjusting die is from a Japan sourced set and says "28." The die adjustment seems good .
 
I don't know if it would apply to your situation at all but I know in old Volkswagens they use a metric thread for sensors very close to 1/8npt. It's close enough that lots of people just put the npt into the metric hole without knowing its not the same thread. But I can't remember the size of the metric one off hand so its not much help.
 
Here's the latest. The auto forum guys (familiar with this problem) sent me a source which sells a "T" fitting. The block takes 1/8 BPT male with two 1/8 NPT females provided for the common aftermarket sensors. ( Why did Toyota select a Brit thread?). I "resized" the new male sensor from its identified 1/8 NPT to "something" smaller which "worked." I say "something" because the reduction in diameter is around .020" and it hand started and felt good tightening to what felt "typical" pipe thread torque. What still is a little mysterious is the smaller diameter of the Japan sourced, solid die stamped 1/8 NPT. Perhaps it is really BPT. The Japan die set contains both a 27 and 28 gauge. Perhaps I have (so far) gotten by with a smaller 28 thread entering a 27 pitch female and the wedging did a handshake. Thanks for the comments and hope this helps someone.
 
I ran across the same thing a few months ago with some Bijur type oiling system parts that came from Asia. Wow, what a mess, I wound up buying a set of taps and dies for BSP threads, and they are smaller in diameter. Tried the dies and taps and yep, they fit to a tee. That reminds me, I need to get back to that project.:(
 
Last edited by a moderator:
I wondered:
Is BSP thread same as NPT?

BSPT (British Standard Pipe Thread) is similar to NPT except for one important difference. The angle across the flanks of threads (if you sliced the fitting in half long-ways and measured the angle from root to crest to root) is 55 degrees instead of 60 degrees as it is for NPT.

Pipe tap.jpg
I thought the 1/8 NPT would be smaller overall than the 1/8 BPT?

..the new sensor measured .020" larger along the taper
..The aftermarket sensor has a label "1/8 - 27 NPT
..have been told there that the block thread is BPT

Question: Why would the mighty Japanese auto industry adapt a BPT? Answer: European market.
Question: Why is there variation die to die? Answer: Being tapered.

What still is a little mysterious is the smaller diameter of the Japan sourced, solid die stamped 1/8 NPT.
Would that not be dictated by the small end of the die?
 
LucknowKen said:
I wondered:
Is BSP thread same as NPT? (No)

Question: Why would the mighty Japanese auto industry adapt a BPT? Answer: European market.
Question: Why is there variation die to die? Answer: Being tapered. (BPT was my mistake. Should be BSP. Answer your question on why BSP and not NPT, BSP is more widely used than NPT, World wide.)

What still is a little mysterious is the smaller diameter of the Japan sourced, solid die stamped 1/8 NPT.
Would that not be dictated by the small end of the die? (My die is stamped "R 1/8" and the tap is marked "RC-1/8")
Click to expand...

See my remarks above in red.
 
LucknowKen said:
Would that not be dictated by the small end of the die?
Click to expand...
If you meant tap instead of die, then yes, exactly. I have had to trim some of the taper off BSPT taps to get enough thread engagement using standard fittings in blind holes The angle grinder is your friend in these situations.
John.
 
You must log in or register to reply here.
Back
Top