The package of machine heads include the necessary tiny mounting screws as well as the decorative chrome colored grommets. The grommets measure at about 5/16 inch in diameter so I used a letter 'O' drill bit to make the mounting holes. Instead of pounding them into position I used a 'C' Clamp and pressed them into the holes. The pilot holes for the screws that hold the machine heads in place were drilled with a #50 drill making them easy to screw into place using a small Phillips head screwdriver - i was concerned about stripping the slot for the screwdriver if the pilot hole was too small. As I recall, the description for the set of four mentions that 2 right and 2 left machines are included and such was the case thus allowing all four to be turned in the same rotational direction to adjust string tension no matter which side of the peg head they are mounted on. Very nice and smooth to use. So far they hold the tension accurately from day to day.