To make an inexpensive drill stop, for a no-mar finish, I used RC model fuel line tubeing. It comes in small sizes 0.40-3/32 0.30 -/8 0.20-5/32 0.10- 3/16. You can get all the different sizes at any RC model shop for about a dollar. You can cut each drill stop to any lenght for a set drilling depth.;)