allowing for a bit of slack then either 7/16" Whit or 3/8" BSF have a 0.82" AF against your 13/16" (0.813) spanner so just need to check the OD of the thread.

Just put "nut AF sizes" into your search engine

Edited By JasonB on 27/06/2015 07:31:56

Hi Capnahab, spanners don't normally fit exactly snug on the size nut they are made for and there is always some amount of slack. The slackness varies from one manufacturer to another and ring spanners very often have a little tad more than open ended ones. A 13/16" AF spanner should fit a 9/16" unified (UNF & UNC) nut/bolt, however it will fit a 1/2" BSW or BSF nut/bolt. On an old spanner, you may well see the spanner marked as 7/16" BSW/1/2"BSF as shown in the photo below.

In this photo is a 1/2" whit bolt with a clearance for a 0.2mm feeler gauge, but in the next photo is the same nut in a 13/16" AF spanner but it will only accommodate a 0.05mm feeler gauge.

So if you can only get a similar feeler gauge or smaller or none at all in with you 13/16" AF spanner, then your nuts are most likely 1/2" BSW or BSF, you will need to find out the diameter of the bolt and the TPI.

It is also possible that your nuts are old enough to be from before Whitworth nuts/bolts were reduced down to the same size as BSF in which case they could be 7/16"BSW.

Regards Nick.

Edited By Nicholas Farr on 27/06/2015 21:00:36

Hi Duncan, yes 1956 was past the time of reduction, but they did seem to linger in stores stocks for quite some time. In a previous employment the stores still had a verity of the old ones as late as the 1980's.

Regards Nick.

Hi Bazyle, you can get BSW & BSF at most industrial suppliers that sell nuts and bolts and failing them they are available at **LINK** although they are zinc plated. Just scroll down to Nuts and then choose Hex Full >

Regards Nick.

> 58 years worth of castor oil crud

I bet it has the consistency of tar by now – but smells nice

Neil

Interesting to see the details of a big top end lathe. For the rounded nut laboriously file new flats each side using old credit card to protect the cast iron.

Thanks for the link Nick, yes I do realise that imperial kit is available but look at the price, and those guys don't list BSW. Intersting in that yesterday I was derusting some some 1/4 BSF bolts thinking it was hadly worth the bother but I see they are 86p each and the nylocks 46p. So Ican see why you don't want to buy both BSF and BSW selection to cover both angles. You could check another similar bolt that you can extract to see if they considered it acceptable to tap cast iron with a fine thread.

.

Quite so … and here's another thought: I have not had the pleasure of inspecting a DSG lathe, but it looks to me like those nuts must be on Tee-Bolts working in a circular track [square section or dovetailed].

From what I can see in your picture, my guess is that they are 3/8" BSF. or maybe 'later-version' 3/8" BSW … , either of which should be reasonably easy to find.

If all else fails, you could probably drill into a face of the nut, and then split it with a sharp Cold-Chisel … should unscrew very easily then.

MichaelG.

Good work, Capn'

So … are they 3/8" BSF, or what ?

MichaelG.