Metric Threads

Prior to utilizing the TT2″, a pre-hole must be punched.  For best results, always tap the holes in the same sequence as the pre-holes are punched.  This will eliminate any backlash that is in the punch press.

The necessary pre-hole punch sizes are listed on the chart below. This chart is based on 65%-70% thread. For every .001 difference in hole size the % of thread changes by 5%.

The pre-hole punch sizes listed on these charts are for both extruded and thru-holes.  For extruded hole size use flat material pre-hole.  If multiple pre-hole diameters are listed, use 0 – .080.

WARNING – Do not exceed .002 smaller pre-hole size than required. Serious tool damage may result.

Metric Thread / American Punches

Tap Size Material Thickness Punch Size
M6 x 1.0 0 – .090 .219
M6 x 1.0 .100 – .250 .221 – .223
M8 x 1.25 0 – .090 .293
M8 x 1.25 .100 – .250 .295 – .298

Metric Thread / Metric Punches

Tap Size Material Thickness Punch Size
M6 x 1.0 0 – 2.28mm 5.52mm
M6 x 1.0 2.54mm – 6.35mm 5.61mm – 5.66mm
M8 x 1.25 0 – 2.28mm 7.44mm
M8 x 1.25 2.54mm – 6.35mm 7.49mm – 7.56mm

Please note:

  • When tapping stainless steel increase the hole size by .001 -.002 on material .07 (1.75mm).
  • Please note that the pre-hole size changes when tapping certain threads on material .09 (2.5mm) or thicker.
  • A smaller H or D factor tap may be needed if tapped hole is too loose. Please see Tap Factor page for further explanation.
  • If tapping extrusions pre-hole is determined by material thickness not thickness of extruded hole.

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