Hex key, length, key depth and tap drill for inch hex socket pipe plugs (pressure plugs), NPTF taper thread.
A socket pipe plug — also called a pressure plug — closes a tapped pipe-thread hole and is turned with a hex key. The threads are NPTF taper threads. The size is the pipe size of the hole it closes (a 1/8″ plug fits a 1/8″-27 pipe-thread hole), not a measurement of the plug. Two kinds: the Dryseal (3/4″ taper per foot) is longer and the more common one; it engages more threads and fits holes that aren’t tapped as accurately. The flush type (7/8″ taper per foot) is shorter and is meant to sit level with the top of the tapped hole.
Socket shown dashed.
| Pipe size | Threads / in | Hex key | Length L | Key depth T min | Tap drill* |
|---|---|---|---|---|---|
| 1/16″ | 27 | 5/32″ | 0.312 | 0.140 | 15/64″ |
| 1/8″ | 27 | 3/16″ | 0.312 | 0.140 | 21/64″ |
| 1/4″ | 18 | 1/4″ | 0.438 | 0.218 | 27/64″ |
| 3/8″ | 18 | 5/16″ | 0.500 | 0.250 | 9/16″ |
| 1/2″ | 14 | 3/8″ | 0.562 | 0.312 | 11/16″ |
| 3/4″ | 14 | 9/16″ | 0.625 | 0.312 | 57/64″ |
| 1″ | 11½ | 5/8″ | 0.750 | – | 1-1/8″ |
| 1-1/4″ | 11½ | 3/4″ | 0.812 | 0.437 | – |
| 1-1/2″ | 11½ | 1″ | 0.812 | 0.437 | – |
| 2″ | 11½ | 1″ | 0.875 | 0.437 | – |
*Tap drill when the hole is finished with a tapered pipe reamer. A dash means our two sources don’t agree — give us a call at 405-670-1234.
| Pipe size | Threads / in | Hex key | Length L max |
|---|---|---|---|
| 1/16″ | 27 | 5/32″ | 0.250 |
| 1/8″ | 27 | 3/16″ | 0.250 |
| 1/4″ | 18 | 1/4″ | 0.406 |
| 3/8″ | 18 | 5/16″ | 0.406 |
| 1/2″ | 14 | 3/8″ | 0.531 |
| 3/4″ | 14 | 9/16″ | 0.531 |
Larger flush plugs: give us a call at 405-670-1234.
Quick answers
- What size hex key fits a 1/8" pipe plug?
- A 3/16″ hex key (Allen wrench) for a 1/8″-27 socket pipe plug.
- What hex key goes with each socket pipe plug size?
- 1/16″ – 5/32″, 1/8″ – 3/16″, 1/4″ – 1/4″, 3/8″ – 5/16″, 1/2″ – 3/8″, 3/4″ – 9/16″, 1″ – 5/8″, 1-1/4″ – 3/4″, 1-1/2″ – 1″, 2″ – 1″.
- What does the size of a pipe plug mean?
- The pipe size of the hole it closes — a 1/8″ plug fits a 1/8″-27 pipe-thread hole. It is not a measurement of the plug.
- What tap drill do I use for a 1/4" pipe plug?
- 27/64″ when the hole is finished with a tapered pipe reamer.
- What is the difference between a Dryseal and a flush pipe plug?
- The Dryseal (3/4″ taper per foot) is longer and the more common one; it engages more threads and fits holes that aren’t tapped as accurately. The flush type (7/8″ taper per foot) is shorter and is meant to sit level with the top of the tapped hole.