Knob Cutter Branch Cutter Mu Tian Bonsai Tools Concave Cutter Round Edge Cutter 205 Mm (8") Material is 4Cr13MoV (Stainless Steel Tool) and High-Carbon Alloy Steel (Carbon Steel Tool), handmade by professional technicians from TianBonsai. Hardness is over HRC55, also with high intensity, strong tenacity and wearability. Hardness is over HRC55, also with high intensity, strong tenacity and wearability.