A quality 3/8" spring washer. This size is commonly used to fix the BPF1B type fuel injection pump in place on the Lister CS engines but could be used for any application requiring this size of Whitworth spring washer.
Top quality M10 brass washers.
These washers can be used under the brass dome nuts on Lister D engines making them suitable as replacements for Lister P/N S545 of which 5 are fitted to the Lister D cylinder head.
They are a smidgen tight on the 7/16" studs being that they are metric but can be teased on without too much difficulty given a little light filing and are the only practical solution now that imperial brass washers are so scarce.
Top quality M12 brass washers.
Top quality M8 brass washers.