Clifton Bench Plane Blades are cryogenically treated .01 steel hardened to HRC60-62. All bench plane blades are made 3.6mm thick to increase rigidity and then accurately ground, embossed with the brand name, and individually checked for hardness. Wipe with oil after use to protect from rust and finger marks. Fits No. 4 & No. 5 Planes - 2" (50mm).