Hi Jeff,

The standard derailleur mounting bolts (both Campy and Shimano) are M10 x 1 (10mm diameter, 1mm between threads). My '72 P15-9 came with the Le Tour GT300 (Shimano Crane) RD, and I replaced it with a 2006 Campy Record long cage; both derailleur mounting bolts fit the Campagnolo dropout derailleur hangar bolt hole perfectly. I've never seen a derailleur mounting bolt with any other threading (not saying they don't exist).

Attached are photos of the bolt from the Crane derailleur and the derailleur cable guides.