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.
|Tap Size||Material Thickness||Punch Size|
|10-24||0 – .080||.172|
|10-24||.090 – .125||.173|
|10-24||.125 – .190||.174|
|10-32||0 – .080||.176|
|10-32||.090 – .125||.177|
|10-32||.130 – .160||.178|
|12-24||0 – .080||.198|
|12-24||.090 – .125||.199|
|12-24||.130 – .190||.201|
|12-28||0 – .090||.200|
|12-28||.090 – .180||.201|
- 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.