Yeah, Ford I had just dropped a inverted 45-70 into the recess and guessed it to be an A base.

@ 0.25" - 0.525" Diameter
@ 0.50" - 0.500" "
@ 0.75" - 0.500" "
@ 1.00" - 0.480" "

Cheers,

Raimey
rse