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|
- 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.