Besly Cutting Tools, Inc., 520
Blackhawk Blvd #135,
|
Besly Drill Selector for Modern Application Taps Fractional Sizes* |
||
|---|---|---|
|
UNC/UNF Threads ASME B1.1-1989 Tap Size and TPI |
Drill Size |
Min. Hole Size (for nickel and titanium alloys) |
| 1/4-20 | 5 | .2055 |
| 1/4-28 | 7/32 | .2188 |
| 5/16-18 | 6.70mm | .2638 |
| 5/16-24 | 7mm | .2756 |
| 3/8-16 | 8.10mm | .3189 |
| 3/8-24 | 8.55mm | .3366 |
| 7/16-14 | 9.50mm | .3750 |
| 7/16-20 | 10mm | .3937 |
| 1/2-13 | 11mm | .4331 |
| 1/2-20 | 29/64 | .4531 |
| 9/16-12 | 31/64 | ..4844 |
| 9/16-18 | 13mm | .5118 |
| 5/8-11 | 13.80mm | .5433 |
| 5/8-18 | 14.60mm | .5748 |
| 11/16-11 | 15.60mm | .6142 |
| 11/16-16 | ** | .6325 |
| 3/4-10 | 16.75mm | .6594 |
| 3/4-16 | 17.60mm | .6929 |
| 7/8-9 | 49/64 | .7656 |
| 7/8-14 | 13/16 | .8125 |
| 1-8 | ** | .8880 |
| 1-12 | 23.50mm | .9252 |
| 1-14 UNS2B | 15/16 | .9375 |
|
* Principle factors which
influence the minor diameter tolerance are ease of tapping, standard drill
sizes, and height of engagement. When tapping difficult-to-machine
materials, the height of engagement may be shallower and still develop
stripping strength greater than the external thread breaking strength. In
these instances, the minor diameter may be increased to the maximum
tolerance to reduce the possibility of tapping difficulties. Refer to the following publications for specific information on limiting dimensions for internal screw threads: ● ASME B1.1-1989, UNIFIED INCH SCREW THREADS. ● FED-STD-H28, FEDERAL STANDARD SCREW-THREAD STANDARDS FOR FEDERAL SERVICES. ● DRILLED HOLES FOR TAPPING BY THE UNITED STATES CUTTING TOOL INSTITUTE ** Recommend using either a special drill or reaming the hole to Min. Hole Size. |
||