How would you replace die-cast tuners? Since machineheads all have a different size. Or do you just go for a safe bet?
Long post coming....
The sizes are actually pretty standard - they nearly all need a 10mm hole through the headstock (Sperzels and Planet Waves need 10mm all the way through, with the others you may find the hole is 10mm at the back and a little smaller on the face of the headstock).
Matching up screw holes is a little trickier. If the screw is on a "tab" at a 45-degree angle to the body of the tuner, then the appropriate Schallers, Gotohs or PWs will all
just about line up.
If they're 3x3 tuners with the screw tab directly below the body of the tuner, then the appropriate 3x3 Gotohs, Grovers, PWs or even vintage Kluson types all, again, just about line up with the screw holes.
Some tuners have a little pin on the body of the tuner to hold it in place, rather than a screw. Sperzels have one pin, Fender/Schallers have two, some other Schallers have one! I think some Wilkinson tuners use this method too. In those cases, you need the same make of replacement tuner, unless you don't mind drilling extra holes.