Hi Peffie - Several years ago I did mugs for my grandchildren. If you are using what I used the plastic cup inside the outer cup pops out and the vinyl weave fits in between the two when the inner cup is popped back in place. Yes they need to be handwashed. I would measure the inside area of the cup to see what the circumference is and then measure the vinyl weave to check on the overlap. A lot will depend on what the pattern is you are using. If it covers pretty much the whole piece of vinyl you will want to be careful with your overlap but if it is all on one side you will be ok with the overlap. The vinyl will be held in place by the two cups coming together. I hope this makes sense and helps. Maybe some of the other chatters will come on with more tips.
cheryl

I have done four and Cheryl is right on the money. I keep a stash because they make a nice last minute gift. Have fun! Pam

Thank you, Cheryl. I intend to adjust the pattern to allow for overlap. It appears the overlap is about 1/2". When the stitching is done and the cup is being assembled, does it just overlap and nothing more is needed? Is it supposed to overlap?
Phyllis