Identifying a screw thread

I have been asked to make a new nut for an old bucket fire pump dating back to the early 1900's. the od of the thread is 9/16" and is 14 tpi. Can anyone give me a clue what thread this is?

It might be BSP. Looking at Kemps Engineers Year-Book B.S.2770, dated 1957, the following diameters are given for 14 tpi BSP - 1/2", 5/8", 3/4" & 7/8". To be certain you will need to know the angle between the thread flanks, 55 degrees. This is difficult to measure with confidence and I leave it to others to suggest a good way.

However given the date I fear it could be anything made up by the makers.

Are you hoping to find a tap to cut the thread in the nut?

JA

Edited By JA on 01/12/2016 16:53:14

A quick 'google' shows that 9/16 14tpi taps are available from the far east/auction sites and not that expensive.. might just be worth the punt on buying one and seeing if it fits. If it doesn't then it's not going to be 60 deg.

Given a decent set of screw gauges it's possible to spot the difference between 60 and 55 degrees by holding the part and correct tpi etc up to a brightish light. It ideally needs sets covering un,bs and metric.

If nothing works out it's possibly un angles and bs pitch or some other combination like that. Usually done to get people to buy something rather than make their own. Some gauges will cover none standard pitches though, What I find is that if it's the correct guage they fit perfectly along the gauges entire length.

John

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Possibly 9/16 uns ( unified special ) that was the only one i could find with 14tpi , you need to determine if the male thread is 55 or 60 degrees or something else .

How did you determine the thread pitch ?

If you used the 14 tpi gauge in a unf/ unc thread gauge set and it matched perfectly then it is a 60 degree thread like all unified threads but if you can see the flanks of the thread and thead gauge don't quite match it could be 55 deg Whitworth , another clue although not always perfect is that Whitworth threads have radiused thread crown and roots but unified are truncated or,flattened off .

On a thread that big you can see quite easily if there is a miss match .

If you have access to a lathe that can cut inch threads you could custom grind an internal thread cutting tool and use the lathe he to cut your thread .

Ian.

I see this query all the while and on something this old it basically lost in time.

Threads are a calculation based on diameter and pitch which determines depth etc so it's quite possible to have 13mm x 10 tpi [ that's a Myford standard BTW , I have the tap to prove it, and the 1/2" x 2.5mm pitch

That's the nice thing about standards, where are so many of them....................]

Was there a "Railway" thread 1900 ish ? I was given a bag of engineering tools by an elderly man , he said they were his fathers or grandfathers.. "who worked on the Railway" Large square dies with 4 hardened cutters ,inserts , like tungsten maybe, makers name and a large R stamped into it . Lots of square tapered flat drills ,dividers etc

55 degrees or 60 degrees -- it's not real critical, as anyone who has ever screwed a BSW nut onto a UNC bolt knows.

Get yourself one of those taps with the same diameter and TPI and you should be good to go. If it needs to seal water etc, a bit of teflon thread tape will make up any difference.

product made in the Uk around 1900,one can be 99% certain it will be Whit form 55degrees,pipe thread pitches were also commonly used with any diameter to suit the pitches, I find a lot of Whit form,19,14,and 11 TPI and occasionally 28 tpi on full size steam and oil/gas stationary engines, convenient to use ,only three sizes of chaser required,no confusion with varying thread types in those days,O/dias easily threaded on the lathe,or pipe threading machines, inside dias tapped in small sizes and screwcut on larger sizes,taps easy to make in company toolrooms ,One example comes to mind ,the eccentric driven valve rods on early Gardner gas engines use BSP thread and pitch on a standard diameter steel rod e.g. 1/2 inch dia . I have often thought when screwcutting BSP why did they not select even threads instead of 19 and 11 it would have saved a lot of time waiting for the screwcutting dial to get to the correct position.

Could it possibly be a worn BSP thread, made with well rounded crests? It would certainly be worth screwcutting to acheive a good fit.

Edited By Brian Hutchings on 02/12/2016 08:21:13