From 1/4" to the standard 2 1/8" size, an absolute must for anyone expanding their joinery. The cutters are very well made and the transparent case with handle completes the excellent price-performance ratio. With individual headers, it is too easy to lose track. Shop is always easy to find. I took a closer look, including some of my favorite spots. Woodcraft and Highland. it's as good as it gets. You don't need carbide unless you are CNC hardwood. The hexagonal rods are the bees' knees. Cartridge never slips. Highly recommended.