Cyliner door lock measurments

[DIYspanner]

These locks are measured for example 45mm/50mm.

Which is the internal measurement and which is the external measurement?

I'm confused and can't see any clear guidance.

 

[crank39]

Unless its an anti snap cylinder where you'd obviously want the anti snap on the external side then it doesn't matter as basic cylinders are reversible, when ordering an anti snap cylinder the vendor will ask you which measurement is the external side i.e. ext 45mm/50mm int

 

[DIYspanner]

Thanks for the information, much appreciated.