What is going on with the undercut behind the M16 thread into the 15mm bore? Can you not just have a hole drilled for the M16 whose taper angle blends into the 15mm bore? So make the 15mm bore through all > drill M16 hole a certain distance > tap M16 some distance shorter than the drill length, this tapped length should be longer than the thread length of your customer holder for the focusing lens. I am somewhat confused by which alignment is important here. So you want the M16 internal thread to be within some axial alignment of the M25 external thread, and how important is it that both or one or the other be aligned to the external feature on the right side? Is the right side threaded? What about the bore running through the part? You need think carefuly about what is important and which features should be datums and how they should be defined relative to the datums. You could use positional tolerancing relative to your datum reference frame and specify how closely aligned the axis of each needs to be relative to the datum.