23/64ths by 32 TPI Thread

[Wendelspanswick]

I've got a knackered thread on my WP 26 tig torch, I took a punt by eyeballing at a M10*1 thread and bought a bolt to make a tap out of as its only copper. On closer inspection (digital calipers and thread gauge) it's 23/64ths by 32 TPI!
I found a tap on ebay for £6 but a new torch body is only £12 so using a spare torch till the new one comes.
Just curious as to what thread form the above is from as its in none of my reference books?

 

[zzr1200]

Sounds a bit like BSA they apparently invented their own thread pitches at times...

 

[hotrodder]

WP17, 18 & 26 are (or should be) 3/8" 32tpi (UNEF, unified extra fine). WP9 and 20 are 5/16" UNF

 

[Wendelspanswick]

Outside diameter of backcap was measured at 9.16mm or 0.360", perhaps it is just undersized.

 

[mike 109444]

Take a look (with magnifying glass) at the tips of the thread to see if they are full form ie do they have the tops of the thread "worn" hence the loss of .015". That would account for the under size.

 

[Wendelspanswick]

Had a look in my collection of taps and drawn a blank for any UNEF, if I can be bothered I will turn up one on the lathe otherwise I will chuck it in the bin.
Thank you all for your help and input.

 

[Wallace]

If anyone needs a 29/32" UNEF tap I have over 50 new ones in the shed!

 

[hotrodder]

Checked some of my backcaps/collet bodies today, all are undersize including a brand new genuine weldcraft gas lens body. I'm guessing it's done due to the extremes of temperature i.e. changing a tungsten etc when the torch is 'kin hot