A5. 10x1 male spigot right
Links to photos of examples:
1976 Itom Automatic
1978 Safari Super Extra
1979-89 Di Blasi R7 #141 on left side
1989-97 Di Blasi R7TB #141 on left side
1996 Di Blasi R7 original
Any top-tank model, with a 10 x 1 threaded hole on the left side (and nothing nearby) would use this A5 petcock.