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.
Inches:
| Tap Size | Material Thickness | Punch Size |
| 2-56 | ALL | .078 |
| 4-40 | ALL | .101 |
| 4-48 | ALL | .103 |
| 5-40 | ALL | .114 |
| 6-32 | ALL | .124 |
| 6-40 | ALL | .127 |
| 8-32 | ALL | .150 |
| 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 |
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.
MD Technology offers the latest technology for automating your tapping applications.
