Correct there, Rex.
Now another conundrum. My parts catalogues, '49-'53 and '54-'57 carry identical diagrams of the Plunger Assembly, neither show 67 4131. My bike did not have this part fitted, neither is it listed or described in Drags despite being illustrated.
https://mikesclassiccyclespares.com/product/67-4131 is a link to show what it looks like, looks to be just a plain washer under the spring bottom coil.
I have a rebound spring lower collar to hand, and measuring the lower top hat brim, it's 2.3mm thick.
This lower collar 89 4258 has a bore of 1", same nominal size as the OD of the Plunger Column. Overall height is 9.4mm, reduced diameter to fit inside the rebound spring coils is 33.5mm. Overall diameter of the brim is 42.7mm
But as suggested, a simple turning job, dimensions to fit the springs, covers and column, with a running clearance where necessary on the column.
Just noticed BSA offered a sidecar spring in the early catalogue, not in the later edition, and true to form there are errors in Drags' parts listing, typically, A,B,M, '49-63 and top collar 89 4257 is not listed or described. As for back order, reckon lead time is until Hell freezes over.....
Swarfy.
