joining to old copper pipe

[madeinthenorth]

I need to tee off a 45year old copper pipe for a new shower.
It looks like 15mm pipe, but is there a risk that speedfit or compression fittings will not seal if the pipe is an old imperial size?

Also same for a tee off a 22mm pipe

 

[croydoncorgi]

Generally speaking, old half-inch copper tube can be used with 15 mm fittings successfully. 22mm fittings will not work so well (or at all) with three-quarter copper tube. You can get adapter olives for compression fittings and converter solder couplings to go from old to new size.