49-56-0072 Milwaukee 1-3/8" Ice Hardened Hole Saw 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 (martensite).  Features:  Ice Hardened cryogenically treated for up to 50% longer lifeOptimized tooth form for up to 2X faster cuttingWide, angled & offset slots for easy plug accessBi-metal construction with 8% cobalt for increased wear resistanceWorks with the following arbors: 49-56-7240, 49-56-7250, 49-56-9100, 49-56-7055, 49-56-7040, 49-56-7140 & 49-56-7150 Specifications:RPM Mild Steel: 250RPM Stainless Steel: 125RPM Cast Iron: 165RPM Aluminum: 375Hole Diameter 1-3/8"