On the early yachts, 1920s, they were the square type for mast and bowsprit. 3/8" wide. This was the same for the early 1930s.

Later in the 1930s the semi-circle type was introduced on the solid yachts with brass ferrules. 3/8" wide.

From the 1930s the hollow yachts were fitted with the square type for mast and bowsprit. 3/8" wide. Smaller yachts had a mini version of the mount for the bowsprit.
Later hollow yachts, Endeavour 3 had semi-circle mast and square bowsprit mounts. The Endeavour 4 was fitted with semi-circle mounts for both mast & bowsprit. Both 3/8" wide with brass ferrules. When the plastic ferrules were introduced, the mast mount widened to 5/16" to take the extra width.
The SY series smaller yachts had square mounts and the 5,6 & 7 had semi-circle mounts and again, when the plastic ferrules were introduced, the mast mount widened to 5/16" to take the extra width.

The SB series had a 3/8" brass tubular mast mounts with "Wavey" sides and fixed by 2 brass screws with the exception of the SB/5 "Western Star" which had a 1/2" brass circular socket type mount fixed by 3 brass screws.

The BR series again had a 3/8" brass tubular mast mounts with "Wavey" sides and fixed by 2 brass screws. Some smaller BR models had semi-circle mounts as fitted to the Endeavour 4.

The RS & RC series had brass tubular mast mounts with "Flat" sides and fixed by 2 brass screws.

This is just a general list as because of the length of production different combinations were possible and did happen.
Early steel mounts were just plain metal, later they were painted either
silver or gold and very late on, they were electroplated brass.