Unknown thread

I've been sorting my taps during lockdown. I’ve come across 3/8th 26 tap. It’s British made. Anyone know what thread it is? Cycle thread?

Cycle or Brass depending on thread angle

If it's a "cycle thread", I'd be interested to know where it went. It might be an old deraillier mounting screw (M10 x1 today). Too small I think for a pedal thread. !/2" & 9/16" UNF If I remember correctly.

Cycle thread was also used on British motorbikes in 1960’s and before that.

All brass threads are 26 tpi exactly the same as ME threads and same thread of 55 degrees as they are British standard.

Cycle threads (CEI ) are 60 degree angle.

Howard

Old models cycle front wheel axle size, 5/16"x26TPI, just making a shaft with an M8x1.0, so close difficult to tell the difference with thread gauges.

Emgee

Edited By Emgee on 19/06/2020 16:16:02

Edited By Emgee on 19/06/2020 16:16:47

The cycle thread would have a rounded crest, the metric would have a truncated crest.

The cycle thread would have a rounded crest, the metric would have a truncated crest. An older cycle rear spindle would have been 3/8"x26tpi, more modern ones will be metric. Just as an aside, the hardware shop in Lampeter still has in stock BSF and Whitworth bolts.

Whitworth bolts are very hard to get over here [Ireland ], I had to make some for a friend to repair his old farm equipment. Just as well I have a collection of Whit and B,S,F taps and dies, never know when they might come in handy.

Concur rear axle cycle thread.

The Cycle threads are indeed a strange mixed bunch, there is a 7/16 X 20 one which is so close to 7/16 UNF that you would have to use an optical comparitor to tell apart.

**LINK**

Rounding and truncating the crest of the thread have the same objective; to prevent interference between the crest of then thread on one part and the valley on the mating part.

For the likes of us, particularly when screw cutting, as opposed to using Taps and Dies (which should do the job for us ), truncation is the easiest method. (IF I search long enough, I could find my Apprentice Training Notes which give the formula to calculate how much to truncate any UNF thread )

Howard