Long Series 5230T.Used for milling keyways and slots. Bright finish. Flute type: 30° helix. Manufactured to BS 122: Part 4: 1980.Inch Tolerances:Diameter: up to 1/2". Tolerance: +0.0005, -0.0013.Diameter: Over 1/2". Tolerance: +0.0005, -0.0015.