Specification:Product Name: Spur GearModule: 1ModuleTeeth Number: 12T / 13T / 14TMaterial:SC45# (Carbon Steel)Surface Treatment:BlackeningInner Bore : 5/6/7/8/10mmNote:The tools is a carbon steel product, and there may be rust on thesurface, but it will not impact the product efficacy and use. Please understand.