Note that the SWD Norton Big 4 already had them as standard fitment from the beginning in 1938.

The sizes are according to the rim size, so WM1, WM2 and WM3.

Here some pictures, there were more makes I guess, and were made by the tyre manufacturers.

I made substitutes from countersunk 5/16" x 1 11/16" WW screws, with the appropriate chrome leather and steel washers and nuts. I only used brass nuts as I had a box full of them, so not necessary.

Hope this helps.

Cheers,

Lex

email (option): welbike@welbi**.net