The acoustic guitar on your bench needs a neck set; you've calculated the neck angle, and carefully trimmed the heel. Now for the step the experts use: pull this special sandpaper between the heel and the body to fine-adjust to a perfect fit.
The 10-yard roll of 120-grit aluminum oxide is ideal for the job. It's canvas-backed for strength so it won't pull apart in the joint, and the handy 1" width saves trimming time in a busy shop.
"This is the best thing for getting a perfect neck-to-body fit on new builds and vintage neck resets. I've used it in my shop for years. Ordinary sandpaper is too weak; it tears on the first or second pull. These cloth backed strips last until the grit finally wears out!"
—Todd Sams, StewMac production manager and veteran guitarmaker/repairman