Machining knowledge, made practicalTap Chart — UNC / UNF ThreadsComplete Unified thread reference from 0-80 to 1-1/2": threads per inch, major, effective and minor diameters, and the recommended tap drill for every size.
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| Tap size | Series | TPI | Major dia | Effective dia | Minor dia (ext) | Minor dia (int) | Tap drill |
|---|---|---|---|---|---|---|---|
| 0-80 | UNF | 80" | .0600" | .0519" | .0447" | .0465" | 3/64" |
| 1-64 | UNC | 64" | .0730" | .0629" | .0538" | .0561" | #54 |
| 2-56 | UNC | 56" | .0860" | .0744" | .0641" | .0667" | #50 |
| 2-64 | UNF | 64" | .0860" | .0759" | .0668" | .0691" | #50 |
| 4-40 | UNC | 40" | .1120" | .0958" | .0813" | .0849" | #43 |
| 4-48 | UNF | 48" | .1120" | .0985" | .0864" | .0894" | #42 |
| 5-40 | UNC | 40" | .1250" | .1088" | .0943" | .0979" | #38 |
| 5-44 | UNF | 44" | .1250" | .1102" | .0971" | .1004" | #37 |
| 6-32 | UNC | 32" | .1360" | .1177" | .0997" | .1042" | #36 |
| 6-40 | UNF | 40" | .1360" | .1218" | .1073" | .1109" | #33 |
| 8-32 | UNC | 32" | .1640" | .1437" | .1257" | .1302" | #29 |
| 8-36 | UNF | 36" | .1640" | .1460" | .1299" | .1339" | #29 |
| 10-24 | UNC | 24" | .1900" | .1629" | .1389" | .1449" | #25 |
| 10-32 | UNF | 32" | .1900" | .1697" | .1517" | .1562" | #21 |
| 1/4-20 | UNC | 20" | .2500" | .2175" | .1887" | .1959" | #7 |
| 1/4-28 | UNF | 28" | .2500" | .2268" | .2062" | .2113" | #3 |
| 5/16-18 | UNC | 18" | .3125" | .2764" | .2443" | .2524" | F |
| 5/16-24 | UNF | 24" | .3125" | .2854" | .2614" | .2674" | I |
| 3/8-16 | UNC | 16" | .3750" | .3344" | .2983" | .3073" | 5/16" |
| 3/8-24 | UNF | 24" | .3750" | .3479" | .3239" | .3299" | Q |
| 7/16-14 | UNC | 14" | .4375" | .3911" | .3499" | .3602" | U |
| 7/16-20 | UNF | 20" | .4375" | .4050" | .3762" | .3834" | 25/64" |
| 1/2-13 | UNC | 13" | .5000" | .4500" | .4056" | .4167" | 27/64" |
| 1/2-20 | UNF | 20" | .5000" | .4675" | .4387" | .4459" | 29/64" |
| 9/16-12 | UNC | 12" | .5625" | .5084" | .4603" | .4723" | 31/64" |
| 9/16-18 | UNF | 18" | .5625" | .5264" | .4943" | .5024" | 33/64" |
| 5/8-11 | UNC | 11" | .6250" | .5660" | .5135" | .5266" | 17/32" |
| 5/8-18 | UNF | 18" | .6250" | .5869" | .5568" | .5649" | 37/64" |
| 3/4-10 | UNC | 10" | .7500" | .6650" | .6273" | .6417" | 21/32" |
| 3/4-16 | UNF | 16" | .7500" | .7094" | .6733" | .6823" | 11/16" |
| 7/8-9 | UNC | 9" | .8750" | .8028" | .7387" | .7547" | 49/64" |
| 7/8-14 | UNF | 14" | .8750" | .8286" | .7874" | .7977" | 13/16" |
| 1-8 | UNC | 8" | 1.000" | .9188" | .8466" | .8647" | 7/8" |
| 1-12 | UNF | 12" | 1.000" | .9459" | .8978" | .9098" | 59/64" |
| 1 1/8-7 | UNC | 7" | 1.1250" | 1.0322" | .9497" | .9704" | 63/64" |
| 1 1/8-12 | UNF | 12" | 1.1250" | 1.0709" | 1.0228" | 1.0348" | 1 3/64" |
| 1 1/4-7 | UNC | 7" | 1.2500" | 1.1572" | 1.0747" | 1.0954" | 1 7/64" |
| 1 3/8-6 | UNC | 6" | 1.3750" | 1.2667" | 1.1705" | 1.1946" | 1 13/64" |
| 1 1/2-6 | UNC | 6" | 1.5000" | 1.3917" | 1.2955" | 1.3196" | 1 11/32" |
| 1 3/4-5 | UNC | 5" | 1.7500" | 1.6201" | 1.5046" | 1.5335" | 1 35/64" |
| 2-4.5 | UNC | 4 1/2" | 2.0000" | 1.8557" | 1.7274" | 1.7594" | 1 25/32" |
Before you tap
Most tap failures start in the pilot hole and end with a seized flute. Get the hole right, then keep the tap cutting.