Clearance hole chart

A clearance hole lets the fastener pass through one part while the threads engage another part or a nut. The right fit depends on alignment, tolerance stack, and how much movement the assembly can accept.

1/4-20 UNC

ACTIVE

Tap size:: 1/4-20 UNC
Recommended tap drill:: #7
Decimal inch:: 0.2010 in

Metric mm:: 5.105 mm
Nearest fractional drill:: 13/64
Thread standard:: UNC

Close, normal, and loose fit

Close fit is used when alignment matters and the parts are controlled well. Normal fit is the common default. Loose fit gives more assembly room when parts are less precise or need easier field installation.

Close fit: tighter location, less room for misalignment.
Normal fit: practical default for many shop assemblies.
Loose fit: easier assembly, more positional movement.

Clearance drill is not a tap drill

The tap drill is smaller because it leaves material for threads. The clearance drill is larger than the fastener diameter because the fastener is not supposed to cut threads in that part.

15 results

Scope: All families Sort by: Tap size Filters

Tap size	Thread pitch / TPI	Recommended tap drill	Decimal inch	Metric mm	Clearance drill	Thread type
10-24	24 TPI	#25	0.1495	3.797	3/16	UNC
1/4-20	20 TPI	#7	0.2010	5.105	9/32	UNC
5/16-18	18 TPI	F	0.2570	6.528	11/32	UNC
3/8-16	16 TPI	5/16	0.3125	7.938	13/32	UNC
1/2-13	13 TPI	27/64	0.4219	10.716	17/32	UNC
10-32	32 TPI	#21	0.1590	4.039	13/64	UNF
1/4-28	28 TPI	#3	0.2130	5.41	9/32	UNF
3/8-24	24 TPI	Q	0.3320	8.433	13/32	UNF
M6 x 1.0	1.0 mm pitch	5.0 mm	0.1969	5	6.6 mm	Metric
M8 x 1.25	1.25 mm pitch	6.8 mm	0.2677	6.8	9.0 mm	Metric
M10 x 1.5	1.5 mm pitch	8.5 mm	0.3346	8.5	11.0 mm	Metric
M8 x 1.0	1.0 mm pitch	7.0 mm	0.2756	7	9.0 mm	Metric Fine
M10 x 1.25	1.25 mm pitch	8.8 mm	0.3465	8.8	11.0 mm	Metric Fine
1/8 NPT	27 TPI	Q	0.3320	8.433	n/a	NPT
1/4 NPT	18 TPI	7/16	0.4375	11.113	n/a	NPT

10-24

UNC

24 TPI

#25

0.1495 in

3.797 mm

1/4-20

UNC

20 TPI

0.2010 in

5.105 mm

5/16-18

UNC

18 TPI

0.2570 in

6.528 mm

3/8-16

UNC

16 TPI

5/16

0.3125 in

7.938 mm

1/2-13

UNC

13 TPI

27/64

0.4219 in

10.716 mm

10-32

UNF

32 TPI

#21

0.1590 in

4.039 mm

1/4-28

UNF

28 TPI

0.2130 in

5.41 mm

3/8-24

UNF

24 TPI

0.3320 in

8.433 mm

TPI = Threads Per Inch. Data is for reference only. Always verify with current tooling standards.

References

Albany County Fasteners clearance hole chart

Popular tap drill lookups

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Tap drill guides

Full chart

Tap drill chart Use the tap drill chart to find drill sizes for UNC, UNF, metric, metric fine, and NPT threads with decimal inch and metric mm values. Open guide UNC tap drill chart Find UNC tap drill sizes for coarse inch threads, including 10-24, 1/4-20, 5/16-18, 3/8-16, and 1/2-13. Open guide UNF tap drill chart Find UNF tap drill sizes for fine inch threads, including 10-32, 1/4-28, and 3/8-24 with decimal and metric values. Open guide Metric tap drill chart Find metric tap drill sizes for common coarse metric threads, including M6 x 1.0, M8 x 1.25, and M10 x 1.5. Open guide Metric fine tap drill chart Find metric fine tap drill sizes for fine pitch metric threads, including M8 x 1.0 and M10 x 1.25. Open guide NPT tap drill chart Find NPT tap drill sizes for tapered pipe threads, including 1/8 NPT and 1/4 NPT drill references. Open guide Tap drill calculator Calculate tap drill sizes for inch and metric threads, then compare the result with common shop drill sizes. Open guide Drill and tap chart Match common tap sizes with drill sizes for UNC, UNF, metric, metric fine, and NPT threads. Open guide Drill bit size chart Compare drill bit sizes used for tapping, including fractional, number, letter, decimal inch, and metric values. Open guide Roll tap drill size Understand why roll taps and form taps use larger drill sizes than cut taps, and when to check manufacturer data. Open guide Form tap drill size Find practical guidance for form tap drill sizes and why thread forming taps need a different starting hole than cutting taps. Open guide Pipe tap drill size Find pipe tap drill size guidance for NPT threads, including 1/8 NPT and 1/4 NPT reference values. Open guide What size drill bit for a 1/4-20 tap? For a 1/4-20 UNC tap, the common tap drill is #7, which is 0.2010 in or about 5.105 mm. Open guide What size drill bit for a 10-32 tap? For a 10-32 UNF tap, the common tap drill is #21, which is 0.1590 in or about 4.039 mm. Open guide What size drill bit for an M8 x 1.25 tap? For an M8 x 1.25 tap, the common tap drill is 6.8 mm, which is about 0.2677 in. Open guide

Quick formulas

Metric tap drill formula

Tap drill = major diameter - pitch.

Example: M8 x 1.25 uses 8.00 - 1.25 = 6.75 mm, rounded to 6.8 mm.

Inch tap drill formula

Tap drill = major diameter - (1 / TPI).

Example: 1/4-20 gives about 0.200 in, commonly #7.

Cut taps and form taps

Form taps usually use a larger drill size and create threads by displacing material.

Clearance hole guide

Use clearance drills when a fastener must pass through a part instead of cutting threads.

FAQ

What size drill bit for a 1/4-20 tap?

A common recommendation is a #7 drill bit, which is 0.2010 in or about 5.105 mm.

How do you calculate tap drill size?

For metric threads, subtract the pitch from the major diameter. For inch threads, subtract 1 divided by TPI from the major diameter.

Is tap drill size the same for roll taps?

No. Roll taps usually need a larger hole than cut taps. Check the tap manufacturer data for the material you are working with.

What is the difference between tap drill and clearance drill?

A tap drill prepares a hole for threading. A clearance drill makes a hole large enough for a fastener to pass through.