Metric Thread/Metric Hole Sizing

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 / Metric Punches

Tap Size Material Thickness Punch Size
M2 x .4 ALL 1.83mm
M2.5 x .45 ALL 2.3mm
M2.6 x .45 ALL 2.4mm
M3 x .5 ALL 2.78mm
M3.5 x .6 ALL 3.24mm
M4 x .7 ALL 3.69mm
M5 x .8 0 – 2.03mm 4.65mm
M5 x .8 2.28mm – 3.17mm 4.7mm
M5 x .8 3.3mm – 4.06mm 4.8mm

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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