How do you determine tap drill size?
John Johnson
Updated on March 18, 2026
As a rule of thumb, for Metric threads, the tapping drill can be calculated by subtracting the pitch from the diameter of the thread. eg for an M5x0. 75 thread the tapping drill is 5-0.75mm = 4.25mm. For Imperial (inch) threads the tapping drill size is calculated in the same way, diameter minus pitch.
What is tap drill size?
a good tap drill is 90% (± 2 pp) of major diameter for fine threads. Therefore, a size 7⁄16 screw ( 7⁄16 ≈ 0.437) with 14 threads per inch (coarse) needs a tap drill with a diameter of about 0.371 inches.
What size drill do you use for a 3/8-16 tap?
5/16
For example, the tap drill for 3/8-16 is 5/16. 3/8 – 1/16 = 5/16. For other sizes that don’t work out so nicely, just use the closest drill size.
What size hole do I drill for a 1/2 inch pipe tap?
| Tap size | Threads per inch | Drill size w/out taper pipe reamer |
|---|---|---|
| 1/2 | 14 | 23/32 |
| 3/4 | 14 | 59/64 |
| 1 | 11.5 | 1 5/32 |
| 1 1/4 | 11.5 | 1 1/2 |
How do I choose a tap drill?
Rules of Thumb A good tap drill is 90% (± 2 pp) of major diameter for fine threads. For metric V threads, the concept of major minus pitch (i.e., the major or widest diameter of the intended screw in millimeters minus the pitch of the threads of that screw in millimeters per thread) yields a good tap drill diameter.
What are the 3 types of taps?
Different Types of Thread Taps
- Straight Flute Taps (Hand Taps) Hand taps, typically bought at the local hardware store, are the most common types of taps, but they are generally to be avoided for CNC work.
- Spiral Point Taps (Bull Nose Taps)
- Spiral Flute Taps (Gun Taps)
- Roll Form Taps (Thread Forming Taps)
Can you use a tap in a drill?
You can use a tap to cut threads in a hole drilled in metal, such as steel or aluminum, so you can screw in a bolt or screw. For safety, it’s also important that you steady the item you’re drilling and you use the right drill bits.
What size drill bit do I use for 1/4 20 tap?
The best overall size drill bit for 1/4″ 20 tap is a #7 drill bit, the measurement being 13/64”. The concept of tapping threads is relatively simple, but in practice, it can get complicated.
What size hole do I drill for a 5/16 tap?
In this case, the most relative drill bit size corresponding to the 5/16″-18 tap is 17/64, which corresponds to an F drill bit.
How big is a 3 / 4 inch tap drill?
tap/drill sizes cont. pipe thread drilled hole sizes tap size cutting taps tru-flo ™ forming taps inch metric drill size decimal equivalent drill size decimal equivalent 3/4-10 21/32 .6562 45/64 .7031 3/4-16 11/16 .6875 23/32 .7188 m20 x 2.50 17.50mm .6890 m20 x 1.50 18.50mm .7283 m22 x 2.50 19.50mm .7677 m22 x 1.50 20.50mm .8071 7/8-9 49/64 …
What’s the correct pitch for a tap drill?
M6 x 1 Thanks to Jay Steinbuchel of Barksdale Control Products for the following: This works for all 75% threads, not just metric. For example, the tap drill for 3/8-16 is 5/16. The pitch is 1/16″. (1 / threads per inch = inches per thread) 3/8 – 1/16 = 5/16. For other sizes that don’t work out so nicely, just use the closest drill size.
How to calculate tap drill size for Acme taps?
3/8 – 1/16 = 5/16. For other sizes that don’t work out so nicely, just use the closest drill size. Tap drill size size formula’s are theoretical based on the thread type and desired percentage of thread. Please allow for the fact that drills generally drill oversize. tap drill size for acme taps. to calculate tap drill size for acme taps.
What’s the drill bit size for a thread hole?
For each thread count, the equivalent thread pitch is provided and for metric taps, the approximate thread count is shown based on the pitch. Lastly, the recommended tap drill size is provided for each standard tap size. This size drill bit should be used for drilling the initial hole that will then be tapped.
