Our handles come from the new owner of Bulldog tools (now called Clarington Forge) They fill fit either the 43 inch Spear and Jackson or the 43 inch Clarington Forge D-handled tools. The handles have a larger diameter these days but seem to fit older Bulldog d-handled tools. (Probably will need some modification)
Shaft diameter = 1.75" Shaft diameter tapers from 1.5" to .75" where it is inserted into the fork. The length of this tapered section varies from 6.75" to 7.75".
We had a local buy one of these handles for a very old Bulldog tool. They had to trim it down a little but were very happy with the result.