Mumbles has it about the H, the 10, and the J.
The Champion H10C is the closest – easily obtained –
replacement I know of. It has the 11.2 mm thread
reach as did the H10C but the end of the ground
isn’t centered over the electrode. A file can change
that if one likes.
Tubs.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.