BSF and Whitworth "Across the flats " sizes.

Am I correct in assuming that the spanner sizes for Whit and BSF are the same.? I realise bolt O/D will differ!)

I have plenty of AF and also Whit spanners. I must have used these on BSF size bolts without realising. A quick check on a couple of BSF bolts seems to indicate that the head sizes are the same as Whit, is this generally true, or have I just been lucky?

Andrew.

Yes.

Of course, you get this funny thing in which pre and post war 'declared' sizes are different because they reduced the size of the whitworth head to one size smaller to save steel. But the range of across-flats dimensions are the same, you only need one set of spanners for bsw/bsf....

Cheers, Colin

Edited By Hillclimber on 07/10/2017 11:46:10

Whitworth and BSF use the same sizes but just forget the markings on the spanner, also if you come across very old Whitworth stuff it will have a larger head as they downsized the heads. This is why the marked sizes on spanners don't make sense.

Mike

Thanks gentlemen!

That will save me buying BSF spanners. Probably not as easy to do these days!

Andrew.

Hello Carl,

Thanks for the caveat. I have some BSF spanners on order!

Regards,

Andrew.

All my Whit/BSF spanners (which date from my motorcycle days in the early 60's) are dual marked with the whitworth size being one smaller than the BSF. eg 5/16 whit also fits 3/8 BSF.

It seems that metric AF sizes also vary eg an M12 nut encountered today which takes an 18 mm spanner rather than the normal 19.

Volkswagen also use odd sizes, you will find a use for that 16mm as well as 18mm, what you thought was torx may also be spline drive, yet another flavour of multipoint drive. You will never have enough tools as long as they keep inventing new drive standards. Once we just had flat blade screwdrivers then Philips came along then Pozidrive then supadrive then square,

Mike

That M12 nut retains the wheel on a Creusen bench grinder.

Mike Poole:

Some time ago I came across an "Allen" screw with a five-sided recess. This design may be intended to be tamper-proof.

iPhone use 5 sided Allen type fasteners, it seems a pointless exercise as almost within hours the tool to fit will become available.

Mike

They are more like a five sided Torx fitting than an Allen fastening.

Have to get my magnifying glass out and have close look.

Mike

Just as an aside, I read somewhere that Mr Whitworth made his original across-the-flat dimensions so oddball because they were designed so the hexagons could be machined out of the limited available range of round bar stock in those days. So the hex dimensions are really based more on the across-the-points measurement and the spanners were made to fit the oddball flat dimensions that resulted.

What would we expect from the guy who designed and built muskets for the American Civil war that had a hexagonal shaped bore down the barrel and would fire only the supplied special hexagonal Whitworth bullets? You think it's a headache having a Whitworth bolt and nut and only AF spanners!

Once upon a time, MEW or ME published a table showing equivalences across W, BSF and Metric bolt heads, Sadly, I can't recall the issue.

Marcus

This table is very useful at a pinch, giving BA, metric, AF, BS and WW sizes from 10BA up to 60mm **LINK**

I think the worst thread size in this respect is probably M12. Depending on standard, it requires 17, 18, 19, 21 and 22 mm spanners. I am curious about one thing though, why does my Britool set have 9 and 15 mm spanners when, as far as I can find, they shouldn't fit anything?

Brian