TV Jones Pro Jet Blocks are used to secure our Universal Mount pickups into Pre-2011 Gretsch Electromatic Pro Jets with stock mini-humbuckers. Side blocks are used for pickup ring/bezel screws to bite into, bottom block screws into the body and is for pickup mounting screws to bite into. Large side blocks can be stacked with small blocks. The Pro Jet Slideshow linked below in Tech Specs is a helpful read.
Check out the Pro Jet Mod Slideshow here