Official Luthiers Forum!

Hello, and a good day to all.
I am new to this arena and have a question which I hope an "old sage" may be able to answer. I am currently working on a project guitar picked up in a trade. The guitar was fitted with low grade machines with a headstock bore size of 10mm. I am interested in fitting this piece with some locking machines (leaning toward Sperzels). I inderstand that the bore for Sperzels is 3/8", slightly smaller than the 10mm. Is it possible to mount the Sperzels into these existing holes?
I thank you for your consideration on this question.

I think you'll be fine. But if they are too sloppy you can do a little trick that I've found to be my favorite. Take a q-tip and soak it in thick CA (super glue) and swab it around the inside of the hole. You might have to do this a couple of times in each hole. Then you can go back and re drill the holes to 3/8".
You're only looking at .047" total, divide that by two and you've only got .0235 on each wall. It shouldn't take much CA to fill that in.

Hello Dr under hill, welcome to the OLF sir!