This is the top nut that was fitted on Norton Sidevalve (SV), Overhead Valve (OHV) and CS1 models - in fact all girder fork models that were fitted with the bakelite Norton type steering damper - the rod of this assembly fitting through this nut. These are CNC manufactured from stainless steel using a genuine Norton nut as the pattern.
As it is now very difficult to obtain the original large Whitworth size hex bar in stainless steel, these nuts are turned and then milled from a solid billet - but the result being a very pretty nut in stainless, that faithfully replicates the original nut and 3/4" Whit hex form.
Sorry this is not the cheapest of items, but the setup costs and the amount of time spent checking original items for fitting reflect the final price. We make this nut from a solid stainless billet (see final photographs) and it required two soft collets to be machined to hold the billets through the different machining operations. However, where the most time was spent, was checking the internal thread of this large nut against original Norton girder fork steering columns - where a large variation in threads was found.
Background Information and Steering Head Thread Chasing:
As you can imagine - any original Norton girder fork steering head will be at least 80 years old now and possibly more. When checking the thread of of original steering heads, we found numerous variations in tolerance, and some steering heads which obviously had a worn or undersize thread. After trying against numerous original steering head threads we found the most common thread tolerance - which resulted in a good smooth fit, but was not too loose, as you can see in the photographs, we then created Stop/Go threaded plugs to ensure the nuts offered in this item meet that tolerance.
Each nut is CNC machined from solid Stainless 303 and the correct imperial hex flat milled. The finish is excellent, and they much improve the finish of your pre-war girder forked model. In the accompanyning photographs I have included an original Norton nut in the normal 'rough' condition, as a comparision to our nut in stainless steel. Our nut is fitted to an original damper assembly (although admittedly - the assembly I used for this photograph had a broken bakelite knob).
Please note: it is important you check your original thread is in good condition before attempting to fit this nut. If the original thread is corroded or ripped (as many original steering columns we checked as part of this manufacturing process were), then it is likely to damage the thread of this nut - and sorry, but once you attempted to do this, we cannot accept Returns.
To help with this - if you have doubts about the condition of your original steering head thread - then the correct 1.125" BSC Die can be obtained from Tracy Tools, see their website at: https://www.tracytools.com/
This can be used to 'chase' the original thread before fitting the new nut. I have used this company for specialist BSC (and other sizes) tap and dies for 30 years and they are excellent.
Final point: As part of this machining process, we did manufacture a couple of nuts with oversize threads (for those steering columns that had bad threads and would need heavily chasing - I had one such column myself). If you think you may require an oversize nut, email us on our normal firstname.lastname@example.org to check for availability.