My crash / badge / oil gauge / clock bar on the KH(A) is based on the Britax bar so the dimensions are similar, although not identical in one or two places. Each bar is 12" long and made from 1.150" hex. The hex is probably what I could find so the dimension may not be the same as the Britax. Starting at the frame end, you have 5/8" circular, then 3/4" hex, then circular again to the hex at the outer end. From memory the hex at the outer end was the same length as the 3/4" towards the frame end, but I made mine a with a bit longer hex at the outer end. The outer end of the bar is radiused. My bars have extra lengths of hex where the instruments are mounted.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.