Thread pitch for knee elevation dial holder

[CulinaryOne]

I bought and am restoring a BP J head mill. During the reassembly, I found that the internal threads on my z axis/knee dial holder are in bad shape. Does anyone happen to know the pitch of the internal threads? I'm planning to buy a tap and see if I can clean up the threads before buying a new one. This is the replacement part i'm asking about, and I'm looking for the pitch on the inside of the part, which threads onto the rod which goes inside the knee to the bevel gear.

1232 - Dial Holder