BSA Twins by D W Munro features a cross section of the early front hub. Edition published in 1960, page 132.
As illustrated elsewhere, by note of explanation, the spindle is plain along it's length, threaded at the brake drum end for the fork slider.
Wheel bearing inner races locate on a central spacer, a very similar arrangement as found on the later S/A crinkle type rear wheel. Outboard of the bearing inner races, a spacer supports the brake back plate and locates against the fork slider. On the left hand end a tubular "distance piece" spacer is carried by the spindle, this tube is clamped by the fork pinch bolt as the final assembly step after the spindle has been tightened and the fork legs have been settled. Reckon this is slit along it's length to grip the spindle as the pinch bolt tightens down, but I may be wrong here.
The spindle length is not critical for a homespun part, depending on what original parts are to hand, but the left hand thread on the end certainly is and a starting point would appear to be an ex single sided brake spindle, or similar part with a left hand thread to fit the right hand fork leg. ... unless clever machining skills are available to start from scratch.
A search of the early parts catalogue in the Forum Literature section will also help, this carries illustrations of the individual parts rather than exploded assemblies as in the later editions.
BSA Service Sheet 212 is the one for this early brake assembly.
Swarfy.
