Identifying an unusual thread: 26 tpi

[Rob Kovacs]

Hi,

I am restoring an old Record model 35 bench vice with 5 1/4" wide jaws. I have removed the screws that hold the jaw plates on to the two mating faces of the vice jaws. I want to replace the screws, as they were badly rusted and the (slotted) screw heads were deformed. I have tried to identify the thread form on these screws, but I am having difficulty.

The outside diameter of the screw is approximately 0.307" to 0.310" (7.78mm) or thereabouts, depending on where you take the reading on the threads. I have used several thread gauges to check the thread pitch, and found it to be 26 tpi. I also checked the screws with the 24 tpi gauge, the 28 tpi gauge and the 1.0mm metric gauge. The 26 tpi gauge was didinitely the best fit over about ten consecutive threads. As the outside diameter of the thread was very close to 8mm, I suspected that it may be a metric fine thread, (M8 x 1.0), but the 26 tpi gauge was a better fit than the 1.0mm, which appeared to be slightly too coarse over the ten threads that I was lining up with the thread gauge.

This vice is old, and made in England. I would suspect that it had British threads, or at least something imperial, like UNF. I have compared the screws to some of the miscellaneous taps that I have, and it is definetely bigger than 1/4", and is not 1/4"-28 UNF or 5/16"- 24 UNF, or 5/16" - 22 BSF. The only Whitworth thread with 26 tpi is 1/4" - 26, but it is definitely not a 1/4" thread.

Does anyone have any idea what this thread is, or any detailed knowledge of what threads were used on Record model 35 (5 1/4" quick-release) vices many years ago?

...totally stumped...

Regards,

Rob

[Rick]

Rob

Could be a British Witworth thread, being it was made in England, There was a 26 pitch thread in the fine series the OD doesn't match up exactly to what you have.

here is a chart for Britch Whitworth threads

http://mdmetric.com/tech/thddat8.htm

[Rob Kovacs]

Hi, Rick,

I had been browsing the Maryland Metric pages for thread info, as they have a lot on just a few pages. That was why I was confused. There are only two threads listed on the Whitworth range with 26 tpi (1/4" and 9/32"), neither of which is close to the 7.8mm (0.310") that I have.

I have been browsing the internet looking for info, but can not find anything on the thread size, or on Record model 35 vices.

Still stumped...

Regards,

Rob

[stevec]

I googled around a bit and was directed to "Irwin Tools" as being the company that took over "Record"
I was trying to see a "model 35" to get an idea if they resembled any of mine. No luck.
BTW I was surprised to see the majority of references were to "vices". I have many but they aren't for workholding .
I thought "vise" was the correct term for the clamp thingy we couldn't exist without .

[John Evans]

As one that has messed about with old British MCs for years I can tell you there were several weird thread types. You apear to have a 5/16 "CEI" 26 thread screw. The CEI series was all 26 thread up through at least 7/16ths as I recall. The good thing is it was a 60* thread . There was about 4 different thread standards used on Brit bikes into the late 60s. BA, BSF,CEI and of course Whitworth.

[JoeCB]

No reason that this would have anything to do with the USA... But I checked into the old ASME standards the closest is a #18 (.294 inch) but that came in 18, 20 and 24 TPI not 26.

Joe B

[Rob Kovacs]

Hi, again,

I have been Googling further, and the only references that I can to a 5/16" - 26 tpi thread are for cycles. There is a British cycle thread of that size, and the American C.E.I. cycle thread (as mentioned above...).

I was just very suspicious as to why a vice (US: vise) manufacturer would use bicycle threads to hold the jaws into the vice. At the time it was made, there were BSW and BSF threads in common use in engineering, so why use a bicycle thread on a bench vice?

Curious...

Now I just need to find some stainless Allen socket cap-head machine screws with that thread on them, as I want to use stainless plates as "soft" jaws in the vice when I re-build it.

Any ideas?

[John Evans]

Well being you are in the home of CEI fastners pop around to a motorcylce shop that caters to Brit bikes and they should be able to fix you up.

[stevec]

Rob, "Now I just need to find some stainless Allen socket cap-head machine screws with that thread on them, as I want to use stainless plates as "soft" jaws in the vice when I re-build it.
"
Since you are "rebuilding" it to you requirements as opposed to restoring it, why not redrill and tap to 3/8-16 or-24 and then avail yourself of std., easy to find, stainless fasteners?

[RichD]

5/16-26 is BSB, British Standard Brass. An all 26 TPI series of sizes. Whitworth form.
Originally used for gas lighting fittings.
I have the set of taps & dies.
RichD, nr Atlanta, GA

[SteveM]

5/16-26 is BSB, British Standard Brass. An all 26 TPI series of sizes. Whitworth form.
Originally used for gas lighting fittings.

Wow, talk about obscure.

Here's some information on it:
http://www.britishfasteners.com/threads/bsb.html

"BRASS THREADS (British Standard Brass)
Because brass tubing has a uniform wall thickness, irrespective of the tube diameter, any thread cut on, (or in) it, would have to have the same depth, so 26 tpi is standard on all diameters. An example would be the thread cut on the brass trumpet horns of the 30s cars, although many were die-cast rather than brass. If it were 1" O/D, the thread would be 1" Brass, 26tpi.

"BSB has a 26 TPI pitch through the whole range and is often confused with BS Cycle thread the difference being that brass thread has an angle of 55 degrees whereas Cycle is 60 degrees. Brass threads are usually confined to fittings and adjusters on cables.
Brass thread taps and dies are sold and advertised as 26 tpi and are identified by the letters BSB.:

Syebe

[RichD]

BSB may seem obscure, but the model engine builders use it along with two pitch
series called "ME" (Model Engineer) having 32 and 40 TPI/55° thread.
1/8" thru 3/8" dia.
Then there is the really strange (to the uninitiated) an entire series of MTP
(Model Taper Pipe) taps and dies for miniature piping. Same taper as standard
commercial pipe, but covering the OD sizes from 1/8" to 5/16".
The 5/16 happens to be identical with 1/16 pipe. All 60° thread form. USA only.
Rich