What is the pitch of a 1/4-20 thread?

1/20 in, which is 0.0500 in or 1.270 mm. The 20 in the designation is threads per inch, so the pitch is its reciprocal.

How do I convert threads per inch to pitch in mm?

Divide 25.4 by the TPI. 20 TPI = 25.4 ÷ 20 = 1.27 mm. To go the other way, divide 25.4 by the pitch in mm: 1.5 mm = 25.4 ÷ 1.5 = 16.93 TPI.

Is thread pitch the same as thread size?

No. Size is the nominal diameter; pitch is the spacing between threads. A 1/4 in diameter appears at 20 TPI (UNC), 28 TPI (UNF) and 32 TPI (UNEF), and only the full designation identifies which is meant.

What does a coarser pitch mean in practice?

A coarser pitch has fewer threads per inch, a deeper thread form and a smaller minor diameter at the same nominal size. That makes it more tolerant of damage and plating but slightly weaker, and more prone to loosening under vibration than a fine pitch.

Thread Pitch Chart

Pitch for every thread series on this site — threads per inch for inch threads, millimetres for metric — and how to convert between the two.

Data verified 2026-09-29 · based on ASME B1.1-2019

Quick Answer

Pitch is the axial distance between adjacent threads. Inch threads state it as threads per inch (TPI); metric threads state it directly in millimetres. They are reciprocals — a 1.5 mm pitch equals 16.93 threads per inch. Pitch is not thread size: the same pitch appears at many diameters.

Find a size or pitch

Thread Pitch by Series

Size^[2]	Series^[2]	TPI / Pitch^[2]	Pitch inch or mm^[1]
M1.6x0.35 #	Metric Coarse Threads	0.35	0.35
M10x1.5 #	Metric Coarse Threads	1.5	1.5
M12x1.75 #	Metric Coarse Threads	1.75	1.75
M14x2 #	Metric Coarse Threads	2	2
M16x2 #	Metric Coarse Threads	2	2
M2.5x0.45 #	Metric Coarse Threads	0.45	0.45
M20x2.5 #	Metric Coarse Threads	2.5	2.5
M24x3 #	Metric Coarse Threads	3	3
M2x0.4 #	Metric Coarse Threads	0.4	0.4
M30x3.5 #	Metric Coarse Threads	3.5	3.5
M36x4 #	Metric Coarse Threads	4	4
M3x0.5 #	Metric Coarse Threads	0.5	0.5
M42x4.5 #	Metric Coarse Threads	4.5	4.5
M48x5 #	Metric Coarse Threads	5	5
M4x0.7 #	Metric Coarse Threads	0.7	0.7
M56x5.5 #	Metric Coarse Threads	5.5	5.5
M5x0.8 #	Metric Coarse Threads	0.8	0.8
M64x6 #	Metric Coarse Threads	6	6
M6x1 #	Metric Coarse Threads	1	1
M8x1.25 #	Metric Coarse Threads	1.25	1.25
M10x1 #	Metric Fine Threads	1	1
M10x1.25 #	Metric Fine Threads	1.25	1.25
M12x1.25 #	Metric Fine Threads	1.25	1.25
M12x1.5 #	Metric Fine Threads	1.5	1.5
M14x1.5 #	Metric Fine Threads	1.5	1.5
M16x1.5 #	Metric Fine Threads	1.5	1.5
M18x1.5 #	Metric Fine Threads	1.5	1.5
M18x2 #	Metric Fine Threads	2	2
M20x1.5 #	Metric Fine Threads	1.5	1.5
M20x2 #	Metric Fine Threads	2	2
M22x2 #	Metric Fine Threads	2	2
M24x2 #	Metric Fine Threads	2	2
M27x2 #	Metric Fine Threads	2	2
M30x2 #	Metric Fine Threads	2	2
M33x2 #	Metric Fine Threads	2	2
M36x3 #	Metric Fine Threads	3	3
M39x3 #	Metric Fine Threads	3	3
M3x0.35 #	Metric Fine Threads	0.35	0.35
M42x3 #	Metric Fine Threads	3	3
M48x3 #	Metric Fine Threads	3	3
M4x0.5 #	Metric Fine Threads	0.5	0.5
M5x0.5 #	Metric Fine Threads	0.5	0.5
M6x0.75 #	Metric Fine Threads	0.75	0.75
M8x1 #	Metric Fine Threads	1	1
#0-80 #	UNC	80	0.0125
#1-64 #	UNC	64	0.0156
#10-24 #	UNC	24	0.0417
#12-24 #	UNC	24	0.0417
#2-56 #	UNC	56	0.0179
#3-48 #	UNC	48	0.0208
#4-40 #	UNC	40	0.0250
#5-40 #	UNC	40	0.0250
#6-32 #	UNC	32	0.0312
#8-32 #	UNC	32	0.0312
1 1/2-6 #	UNC	6	0.1667
1 1/4-7 #	UNC	7	0.1429
1 1/8-7 #	UNC	7	0.1429
1 3/4-5 #	UNC	5	0.2000
1 3/8-6 #	UNC	6	0.1667
1-8 #	UNC	8	0.1250
1/2-13 #	UNC	13	0.0769
1/4-20 #	UNC	20	0.0500
2-4 1/2 #	UNC	4.5	0.2222
3/4-10 #	UNC	10	0.1000
3/8-16 #	UNC	16	0.0625
5/16-18 #	UNC	18	0.0556
5/8-11 #	UNC	11	0.0909
7/16-14 #	UNC	14	0.0714
7/8-9 #	UNC	9	0.1111
9/16-12 #	UNC	12	0.0833
1 1/16-18 #	UNEF	18	0.0556
1 1/2-18 #	UNEF	18	0.0556
1 1/4-18 #	UNEF	18	0.0556
1 1/8-18 #	UNEF	18	0.0556
1 3/16-18 #	UNEF	18	0.0556
1 3/8-18 #	UNEF	18	0.0556
1-20 #	UNEF	20	0.0500
1/2-28 #	UNEF	28	0.0357
1/4-32 #	UNEF	32	0.0312
11/16-24 #	UNEF	24	0.0417
13/16-20 #	UNEF	20	0.0500
3/4-20 #	UNEF	20	0.0500
3/8-32 #	UNEF	32	0.0312
5/16-32 #	UNEF	32	0.0312
5/8-24 #	UNEF	24	0.0417
7/16-28 #	UNEF	28	0.0357
7/8-20 #	UNEF	20	0.0500
9/16-24 #	UNEF	24	0.0417
#0-80 #	UNF	80	0.0125
#1-72 #	UNF	72	0.0139
#10-32 #	UNF	32	0.0312
#12-28 #	UNF	28	0.0357
#2-64 #	UNF	64	0.0156
#3-56 #	UNF	56	0.0179
#4-48 #	UNF	48	0.0208
#5-44 #	UNF	44	0.0227
#6-40 #	UNF	40	0.0250
#8-36 #	UNF	36	0.0278
1 1/2-12 #	UNF	12	0.0833
1 1/4-12 #	UNF	12	0.0833
1 1/8-12 #	UNF	12	0.0833
1 3/8-12 #	UNF	12	0.0833
1-12 #	UNF	12	0.0833
1/2-20 #	UNF	20	0.0500
1/4-28 #	UNF	28	0.0357
3/4-16 #	UNF	16	0.0625
3/8-24 #	UNF	24	0.0417
5/16-24 #	UNF	24	0.0417
5/8-18 #	UNF	18	0.0556
7/16-20 #	UNF	20	0.0500
7/8-14 #	UNF	14	0.0714
9/16-18 #	UNF	18	0.0556

For inch threads the third column is threads per inch and the fourth is the resulting pitch in inches. For metric threads both columns carry the pitch in millimetres.

Pitch vs Thread Size

Pitch and diameter are independent. A 1/4 in diameter exists at 20, 28 and 32 threads per inch depending on series, and a 1.5 mm metric pitch exists at 8, 10 and 12 mm diameters. Specifying only one of the two does not identify a thread.

What pitch controls is how much material the thread occupies: a coarser pitch cuts deeper, leaving a smaller minor diameter and therefore a slightly weaker bolt at the same nominal size, but it is more tolerant of damage and plating.

Converting TPI to Metric Pitch

The two are reciprocals with the unit conversion applied:

pitch (mm) = 25.4 ÷ TPI
TPI = 25.4 ÷ pitch (mm)

So 20 TPI is 25.4 ÷ 20 = 1.27 mm, and a 1.5 mm pitch is 25.4 ÷ 1.5 = 16.93 TPI. The conversion is for reference only — a metric and an inch thread of nominally matching pitch still differ in form and diameter and do not interchange.

Frequently Asked Questions

What is the pitch of a 1/4-20 thread?: 1/20 in, which is 0.0500 in or 1.270 mm. The 20 in the designation is threads per inch, so the pitch is its reciprocal.
How do I convert threads per inch to pitch in mm?: Divide 25.4 by the TPI. 20 TPI = 25.4 ÷ 20 = 1.27 mm. To go the other way, divide 25.4 by the pitch in mm: 1.5 mm = 25.4 ÷ 1.5 = 16.93 TPI.
Is thread pitch the same as thread size?: No. Size is the nominal diameter; pitch is the spacing between threads. A 1/4 in diameter appears at 20 TPI (UNC), 28 TPI (UNF) and 32 TPI (UNEF), and only the full designation identifies which is meant.
What does a coarser pitch mean in practice?: A coarser pitch has fewer threads per inch, a deeper thread form and a smaller minor diameter at the same nominal size. That makes it more tolerant of damage and plating but slightly weaker, and more prone to loosening under vibration than a fine pitch.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	Pitch	derived	For inch threads, pitch = 1 / TPI. For metric threads the pitch is the tabulated ISO 261 value.
[2]	Thread series data on this site	derived	ASME B1.1 and ISO 261 pitch series — see the individual series charts.

Data Sources

Standard	Revision	What it covers on this page
ASME B1.1 — Unified Inch Screw Threads	ASME B1.1-2019	the inch pitch series
ISO 261 — General plan for metric screw threads	ISO 261:1998	the metric pitch series

Cross-checked against:

Pitch values recomputed from the series data and verified at build time

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
Pitch in inches	1 / threads per inch.

TPI and metric pitch are not interchangeable even when numerically close — the thread forms differ.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Thread Pitch Chart." https://refmanual.com/charts/thread-pitch/ (accessed 2026-09-29). Data from ASME B1.1 — Unified Inch Screw Threads, ASME B1.1-2019.

BibTeX

@misc{thread-pitch,
  title        = {Thread Pitch Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/thread-pitch/}},
  note         = {Accessed: 2026-09-29},
  source       = {ASME B1.1 — Unified Inch Screw Threads, ASME B1.1-2019}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Thread Pitch Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/thread-pitch/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ASME B1.1 — Unified Inch Screw Threads, ASME B1.1-2019
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.