any idea on these numbers

[460or338]

my gun is drilled and tapped for a weaver #19 base. but i think a #24 would fit to .are these difference hole wise or somthing else ? also i havnt measured it yet but i think the holes would also be for a 3/8 1913 rail or does only the dovetail come in 3/8 . oh yes what is a dove tail ? .im trying to find a long 1913 rail for what is likely 3/8 holes and not what im guessing at again are standard 7/8 holes