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Collection, Preservation and Display of Old Lawn Mowers

BSW Nuts

1920's Atco Standard 16" restoration.

All the nuts on this machine appear to be oversize BSW. For example the 1/2" BSW has an Across Flats of 1" compared to the standard 0.82" (13/16"). The same applies to all the other sizes. I want to replace all the nuts with new, is there anywhere these larger sizes can be purchased ?  


Keith Wootton Tue, 17/08/2010


Good question although the answer may be trickier! I think you're right about the sizes but that means that it's unlikely that anyone will have new replacements from stock. A good place to try is Jon Cruse at The Mower Centre in Hailsham as he can often supply obsolete parts.

Failing that the alternative is to strip a derelict machine for the parts you need.



hillsider Wed, 18/08/2010

Not sure about the old style nuts but there is no harm in asking around a few nut and bolt suppliers, I have never needed to try them out personally but this looks to be a useful company to try.

Failing that making your own may be an option or enlisting the help of a friend with lathe.

Good luck with the search.



roythegrass Wed, 18/08/2010

Thanks but no luck anywhere. On the existing larger 1/2" BSW nuts I have today been stripping them back to bare metal then polishing and lacquering-they're now better than new!  However this was very tedious as they will have to be brush lacqued again after fixing.  The smaller sizes will be replaced with new as the Across Flats difference is minimal.

As an aside to my original question on all the restored machines I've seen the nuts and bolts have been painted over the same as the frame colour. I stand corrected but I would guess this was highly unlikely during assembly when new. As I'm striving for originality all the fasteners will be bare metal.

hillsider Sat, 21/08/2010

Cleaning up the old nuts is probably the most logical answer but I am not at all sure about them being lacquered. I think most machines would have had them painted along with the rest of the machine.  Hopefully if I am incorrect it will prompt a comment or two from other readers

Even if there is some pitting to a nut after cleaning and treating to halt the corrosion it is all part of the machines history unless of course the amount of wastage of the metal is so great that the nut is unusable.  


gelco1900 Mon, 30/08/2010

I would be more than happy to produce any nuts you require - any size, any shape just let me know what you need.


David Bouchard Sun, 14/09/2014

I read yesterday that during the war they reduced the hex size of all BSW by one step to save on material.  Therefore there is a difference between pre-war and post-war spanner sizes.  The step size was to retain the same set of spanners.

From the front page of this website

"B.S.W. or Whitworth

British Standard Whitworth,an early English thread standard,found on many veteran machines. Threads are coarse,angle 55degrees and the pitch is measured in threads per inch.The size marked on the spanner (half inch whitworth,nine sixteenths whitworth etc) refers to the diametre of the shank of the bolt it fits not the head size and is always in fractions of an inch. For this reason a Whitworth spanner or socket is always larger than AF ones carrying the same size markings.All Whitworth tools will carry a marking,normally a fraction followed by "W", "WHIT" or Whitworth and sometimes  "W/BSF" . Pretty much obsolete by the mid 60s but still found on some cars,motorcycles trucks,trains and machinery made after this. During the second world war the sizes of the heads of BSW and BSF bolts were reduced to save metal,all nuts and bolts were made one size smaller (ie) a 'new' 1/2 whit bolt had the same size head as the old 7/16.The war also emphasised the need for a universal standard in bolt sizes which eventually resulted in the introduction of the 'Unified' system which utilises AF spanners and sockets.
British Standard Fine,in effect,a fine version of whitworth. Size again refers to the thread part of the bolt,not the head. BSF spanners are always marked one size larger than the same sized BSW spanner so for example a 1/4 inch BSW is the same size as a 5/16 inch BSF."