Whitworth Thread Gauge 12G

• This chart says 3/4" is 10 TPI.
• BSW Whitworth Coarse Thread (GB)

3/4" BSF is 12 TPI and 55 degree thread form.

http://www.vdwalle.com/knowledgebase/draad/bsf1.htm

3/4-12 could be Unified Thread Standard. Make and model of the device the shafts on?

Cheers for the replies.

Shaft is fitted to an old (1960-70's) Petter AC2W deisel engine and gearbox fitted to a small boat, I have no idea of original manufacturer of the shaft and coupler.

I think UTS is 60deg, if the thread gauge is to be believed mines definately 55Deg,but thinking about it, it must less than 55 deg to accomodate the 12TPI, threads are also rounded at peaks and troughs as whitworth but i suppose this could be down to its age?

I've got a memory of a thread that had a pitch of 47deg? i suppose it could be this. back to the internet i think.

razor

Have you tried a 3/4" nut on it? It should not be hard to find one. Coat the threads in hard grease or wax to see how the fit went. If it doesn't rattle or bind, it may be ok.

http://www.timebus.co.uk/rlh/whitworth.htm
Yes should be 55º...You might try measuring the width of the shaft, they vary between the BSF and BSW....BSW being 1/8" wider than the BSF, according to this chart....at least that's my take...7/8" for BSF and 3/4" for BSW...

you'll find this invaluable the three wire method

the three wire method plus

plus charts

Hi Razor,

3/4 BSF has all the specs you've encountered, including the relatively big tip and root radii.

Basic effective diameter will be approx 0.6966", with the minor dia. being 0.6432".

Is it a bronze nut on a 304SS shaft?

Stu.

Hi "I've been told that a 3/4 BSW should be 10TPI so perhaps my shaft is BSF"

If you give these details to a good machinist he or she should be able to make you a nut without any problem. If the machinist can not do it with this information then find someone else who has a brain.

Remember that manufacturers sometimes made a proprietary thread to force you to purchase replacements from them. So, if this doesn't match Whitworth standards, it may be a special. Of course this presents a problem to we folks who deal with old stuff.

You could make a wax mold of the threads...This with a micrometer reading of the dia should be enough for the machinist....

3/4" x 10 tpi is ASME B18.2.2

https://www.boltdepot.com/Product-Details.aspx?product=2654&qty=1&gclid=Cj0KCQjwmZejBhC_ARIsAGhCqndubr0zJZGn5Y9P7ivt0kglgVxvIXlZw-khcU0wFbPh0L3jYIjNoOMaAj_IEALw_wcB

https://www.machiningdoctor.com/threadinfo/?tid=84

https://www.gewinde-normen.de/en/12-un-thread.html

If a 3/4"BSF bolt were to hand one could try offering and meshing thread-to-thread to see if there is a fit, perhaps.