The brass Radius Inserts fit in to the Fret Press Caul for smoothly installing new frets, the pack contains 1 x 7.25", 1 x 9.5", 1 x 10", 1 x 12", 1 x 14", 1 x 16", 1 x Flat inserts to cover all the common fretboard radius from vintage and modern Fender and Gibson to classical guitars. The bottom edge is radiused to match the fretboard and has a curved slot that sits over the fret to hold it in place as it is pressed into the fretboard.

The Fret Press Caul has a slot in the bottom to accept the radiused insert and a grub screw to tighten it in place, the shank is 3/8" to fit in an arbor press. Pressing frets with a caul and radius insert is quick and allows you to provide consistent pressure over the whole length of fretwire as you press it in with one smooth motion.