Use this tool to mark your drum shell for drilling. Get the perfect hole distance marked for perfect mounting. The aluminum pencil shaped tool contains 7 inserts. These inserts are pointed in the middle. Use your lug, bracket or spurs to mark the hole positions on your shell. Note: it is best to first place some blue painters tape on the shell, mark a line with a carpenters square, then measure how far from the edge of the shell you would like to place the first hole. Mark that hole with a punch or nail. Now, use your lug with the threaded inserts installed and mark where the second hole will need to be drilled. Now, use a Brad point drill bit to drill your holes. Most lugs require 4mm inserts. Most brackets and spurs require 5mm inserts. If you are mounting a "Trick Drums throw off or but plate, You will need the 10-24 inserts. We sell all 3 sizes for the same price. When you purchase, be sure to tell us what size inserts you want. Please ask if you have questions.