4-1/8" Ice Hardened Hole Cutter Milwaukee ice hardened products utilize a proprietary cryogenic hardening process that improves upon traditional heat treat processes. Unlike surface coatings that wear away, cryogenics harden to the core by minimizing soft metal (austenite) and creating more hard metal (marten site). The result is a product that is more consistently hard throughout, resulting in life up to 50% longer than the competition. Features: Ice Hardened for Longer Life 4" Diameter 120 Maximum RPM Since its founding in 1924, Milwaukee has focused on a single vision: To produce the best heavy-duty electric power tools and accessories available to the professional user. Today, the Milwaukee name stands for the highest quality, durable and reliable professional tools money can buy.