My rear bleed nipples are 3/8 Unf with a 10mm hex head. I have 4 pot Hispec on the front, not sure of the thread size but again the hex head is 10mm.

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10