The String Retainer Block Template is what you'll need if you're using my String Retainer Blocks as a alternative / upgrade for individual string ferrules on the back of your guitar body. User your router to create a perfect recess for the retainer block. Available in Several bridge types (string spacing). Requires a 1/2" guide bushing collar and 1/4" router bit (not included).
1/2" MDF with engraved center lines and reference markings.
Router Guide Bushings 101: A guide bushing mounts to the router's sub-base with a tube that protrudes below. A straight router bit extends through the tube. The outer surface of the tube rides against an edge guide or template, keeping the bit a set distance (offset) from the edge guide or template. (Read the complete article "Understanding Guide Bushings" at Wood magazine)