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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