Needing to buy rings/bases for a Sako 75 Varmint on which I hope to one day put a Swarovski 4-12x50 scope. My question is if the 50mm objective measurement is the outside diameter or is it just the lense diameter - what is the "no kidding" outside objective diameter on this scope? Thanks

50mm is the inner objective diameter. The outside diameter will be somewhere in the range of 56-58mm.
The Z3 has a 1" tube diameter. So you will need the medium-height Optilock rings.

I have a VX-3 4.5-14x50LR Leupold mounted on a Sako 85 Varmint using the "Low" rings. This scope has 30mm tube. The space between barrel objective is about 1.5-2.0 mm.
According to the Sako specs the 1" Low rings build 2mm lower than the 30mm rings. Therefore you will definetly need the medium height rings.

Just measured a Swaro scope with 50mm objective lens. Figure 2.21 - 2.22" outside objective diameter - plus a bit more if your scope has parallax adjustment on the objective (which I believe it doesn't?).

- mike

Thank you gentlemen.