Early Coleman lamp thread question

The filler cap/check valve thread on my newly acquired Coleman Quick-Lite has the following specs:

27tpi x 1/2 OD as close as I can measure it.

I think it could be NPS - National Pipe Straight, or possibly BSYC thread or even a National Special Thread but honestly I'm a little lost and out of my depth. I was looking for a die to clean out the threads as there is a tiny bit of residual lead from the mangled washer.

Does anyone know the specification of Early Coleman lamp threads and can you still get a die for the filler cap thread anywhere?

 

I bought a 1/2-27 UNS tap & die set on eBay. The tap works great for these filler bungs and the die works good for the burner tubes.

 

Never come across UNS threads before but can see it exists. Interesting.

 

I've just found one on eBay and bought it. Thanks for the heads up, Toby!

 

Hope it helps someone

 

Exactly what I wanted to see! This is why a picture is worth a thousand words! Excellent!

 

Earlier Coleman lantern and stoves might have partially adopted the earlier USS thread standard besides having some being customized. Its only later, around the late 40s or after WWII, that the Unified Thread Standard(UTS or UN-threads) superseded the earlier USS.
Nevertheless USS threaded parts are pretty close to those designated as UN or UTS and can be used interchangeably.
Like the metric, they would have the 60° pitch angle. 27tpi on a 1/2" diametre is only available in UNS. 'S' means special, but its still a standard size-pitch on the UN-series.