07 09 07 09 07 09 - Reproduction, even in part prohibited. Printed in UK Modified: 20 June 2023 Reference Table Drill sizes for metric coarse taps. Cutting Speeds Factors which determine the best speed to use in any drilling operations are: 1. Type of material being worked. 2. Diameter of hole. 3. Type of drill. 4. Quality of cut desired. Generally, the smaller the drill the greater the required RPM. In soft material, the speed should be higher than for hard metals. The drill speed for a given drill bit size is according to the table below. Thread Diameter Ø Drill Diameter Ø M2 1.6mm M2.2 1.75mm M2.5 2.05mm M3 2.5mm M3.5 2.9mm M4 3.3mm M5 4.2mm M6 5.0mm M6 5.0mm Thread Diameter Ø Drill Diameter Ø M20 17.5mm M22 19.5mm M24 21.0mm M27 24.0mm M30 26.5mm M33 29.5mm M36 32.5mm Speed Range (RPM) 7240 1410-2270 970-1280 480-580 250-400 180 Sizes in imperial, then metric below Wood 3/8 5/8 7/8 1 1/4 1 1/5 2 9.5 18 22 31.75 41.4 50.8 Zinc Diecast 1/4 3/8 1/2 3/4 7/8 1 6.4 9.5 12.5 19 22 25.4 Alum & Brass 7/32 11/32 15/32 11/16 3/4 5.6 8.75 12 17.5 19 Plastic 3/16 5/16 7/16 5/8 13/16 4.8 7.9 11 16 20.5 Cast Iron & Bronze 1/8 1/4 11/32 1/2 5/8 3.2 6.4 8.75 12.5 16 Mild Steel & Malleable 3/32 5/32 1/4 3/8 1/2 2.4 4 6.4 9.5 12.5 Cast Steel & Med Carbon 1/16 1/8 3/16 5/16 7/16 9/16 1.6 3.2 4.8 7.9 11 14.5 Stainless and Tool Steel 3/64 1/16 1/8 1/4 3/8 1/2 1.2 1.6 3.2 6.4 9.5 12.5 Thread Diameter Ø Drill Diameter Ø M7 6.0mm M8 6.6mm M9 7.8mm M10 8.5mm M11 9.5mm M12 10.2mm M14 12.0mm M16 14.0mm M18 15.5mm
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