Hello Gents
Can someone confirm the following dimensions for me.
As I need to make some rear stand bolts for a needy mate.
Length under the head 1 1/16"
Shaft diameter 7/16"
Shaft length 5/8"
Thread 5/16" 26 TPI

Length of thread =?
Thickness of head=?
Hex diameter=?

Thanks in advance

Hi Darren. I've been given the dimensions by Ray. I'll send you a drawing.

email (option): meck04@bigpond.com

Can anyone confirm correct head size?

email (option): mfarnay@bigpond.net.au

I have measured my NOS WM20 ones and they are 785thou across the flats.
Jeff

So 25/32" (781") if a normal fractional production tolerance is applied (+ or - .015")...Ian

email (option): ian@wright52.plus.com

I believe they are metric at 20 mm like many other M20 bolts. Cheers, Michiel

It could be either 20mm or 25/32"....I have sometimes pondered the reason for the use of a 20mm hexagon size on the BSA, but the fact is it could be either size when a standard engineering production tolerance is applied...

Metric or Imperial?...it's your choice in this case...

It's worth considering that some of the bearing sizes are Metric so that adds to the confusion, as metric options were chosen...Ian

email (option): ian@wright52.plus.com

Further to the above neither size, 20mm or 25/32 A.F., would use a Whitworth size spanner as used on most of the other frame and engine fasteners...

Strange that thy would choose an 'odd' spanner size...It seems to me that 7/16" Whit. (.820 across the flats) would have been the logical choice...Ian

email (option): ian@wright52.plus.com

Thank you gents
It does add to the confusion though,
Another thought is what spanner sizes are in an original tool kit?
My slopers and R35-17 have 11/16" rear stand bolts which suits a 3/8" whitworth spanner

I've come across the old 25/32" af sizes on BSA's before. A65 brake stay nuts are the same. Very odd.

email (option): meck04@bigpond.com

The timing side main shaft nut on the crank and the valve lifter spindle fitting in the barrel are two other examples that come to mind on the M20....

On the subject of anomalies the use of BSF threads on the head bolts and the oil fittings into the crank case stand out as well when the BSA made components are mainly Cycle thread and Whitworth..Ian

email (option): ian@wright52.plus.com

Don't forget the nuts on the footrest rod, which are also this odd size.

email (option): leonhop3_at_planet_dot_nl

That odd size nut or bolt hex (19 1/2mm) appears a lot on pre war and early post war bikes, B31 rear wheel spindle is another example. They must have used this size so they could sell the only spanner that I have found to fit it, that's the bloody useless 15-832. I cut the end off mine and welded it to a 20mm socket. Whenever I make something that replaces that hex I always use .820" hex.

Ian.