THREAD DIMENSIONS FOR ACME AND STUB ACME THREADS

Acme threads are a trapezoidal thread form used mainly for linear motion — lead screws, jacks, valve stems, and vices — rather than for clamping like a standard V-thread. Their wide, flat-topped 29° thread angle makes them stronger and easier to machine than a V-thread of the same size, and far more resistant to stripping under the side loads and repeated cycling typical of a lead screw application. Standard Acme threads use the full 29° trapezoidal profile; Stub Acme threads use a shallower tooth height for applications with limited radial space, at some cost to load capacity.

The charts below provide dimensional information for both Stub and Standard Acme threads. If you need to calculate dimensions for a size not listed, our Acme Thread Calculator will work them out directly, and our universal converter can convert between inch and metric units.

Dimensional Charts for Acme, General Centralizing Acme and Stub Acme Threads.

You can use our Acme Thread Calculator or Stub Acme Thread Calculator to get dimensions for any Acme thread.

Dimensions shown are in Inches, if you wish to convert to mm, please use our universal converter.

ACME THREAD DIMENSIONS

Threads Per Inch	Pitch P	Depth of Thread (basic)	Total Depth of Thread	Thread Thickness	Crest of Nut	Root of Nut Frn=0.03707P	Minimum Depth	Minimum Width of Flat	Maximum Fillet Radius Root of Centralising Tapped Hole	Minimum Classes 5 and 6 Only	Maximum All Classes
Threads Per Inch	P	h=P/2	(all screws)	(basic,) t	(basic)	0.259 x allowance	0.05P	0.0707P	0.06P	0.07P	0.10P
16	0.06250	0.03125	0.0362	0.03125	0.0232	0.0206	0.0031	0.0044	0.004	0.0044	0.0062
14	0.07143	0.03571	0.0407	0.03571	0.0265	0.0239	0.0036	0.005	0.004	0.0050	0.0071
12	0.08333	0.04167	0.0467	0.04167	0.0309	0.0283	0.0042	0.006	0.005	0.0058	0.0083
10	0.10000	0.05000	0.0600	0.05000	0.0371	0.0319	0.0050	0.007	0.006	0.0070	0.0100
8	0.12500	0.06250	0.0725	0.06250	0.0463	0.0411	0.0062	0.009	0.0075	0.0088	0.0125
6	0.16667	0.08333	0.0933	0.08333	0.0618	0.0566	0.0083	0.012	0.010	0.0177	0.0167
5	0.20000	0.10000	0.1100	0.10000	0.0741	0.0689	0.0100	0.014	0.012	0.0140	0.0200
4	0.25000	0.12500	0.1350	0.12500	0.0927	0.0875	0.0125	0.018	0.015	0.0175	0.0250
3	0.33333	0.16667	0.1767	0.16667	0.1236	0.1184	0.0167	0.024	0.020	0.0233	0.0333
2-1/2	0.40000	0.20000	0.2100	0.20000	0.1483	0.1431	0.020	0.028	0.024	0.0280	0.0400
2	0.50000	0.25000	0.2600	0.25000	0.1853	0.1802	0.025	0.035	0.030	0.0350	0.0500

GENERAL PURPOSE AND CENTRALIZING ACME THREAD DIMENSIONS

Nominal Size	Threads Per Inch	General Purpose and Centralizing Classes 2, 3, and 4			Centralizing Classes 5 and 6			Thread Data
Nominal Size	Threads Per Inch	Major Diameter	Pitch Diameter	Minor Diameter	Major Diameter	Pitch Diameter	Minor Diameter	Pitch (P)	Thread Thickness @ Pitch Line (t)	Basic Depth of Thread (h=0.5P)	Basic Width of Flat (F=0.3707P)
1/4	16	0.2500	0.2188	0.1875	--	--	--	0.06250	0.03152	0.03125	0.0232
5/16	14	0.3125	0.2768	0.2411	--	--	--	0.07143	0.03571	0.03571	0.0265
3/8	12	0.3750	0.3333	0.2917	--	--	--	0.08333	0.04167	0.04167	0.0309
7/16	12	0.4375	0.3958	0.3542	--	--	--	0.08333	0.04167	0.04167	0.0309
1/2	10	0.5000	0.4500	0.4000	0.4823	0.4323	0.3823	0.10000	0.05000	0.05000	0.0371
5/8	8	0.6250	0.5265	0.5000	0.6052	0.5427	0.4802	0.12500	0.06250	0.06250	0.0463
3/4	6	0.7500	0.6667	0.5833	0.7284	0.6451	0.5617	0.16667	0.08333	0.08333	0.0618
7/8	6	0.8750	0.7917	0.7083	0.8516	0.7683	0.6849	0.16667	0.08333	0.08333	0.0618
1	5	1.0000	0.9000	0.8000	0.9750	0.8750	0.7750	0.20000	0.10000	0.10000	0.0741
1-1/8	5	1.1250	1.0250	0.9250	1.0985	0.9985	0.8985	0.20000	0.10000	0.10000	0.0741
1-1/4	5	1.2500	1.1500	1.0500	1.2220	1.2220	1.1200	0.20000	0.10000	0.10000	0.0741
1-3/8	4	1.3750	1.2500	1.1250	1.3457	1.2207	1.0957	0.25000	0.12500	0.12500	0.0927
1-1/2	4	1.5000	1.3750	1.2500	1.4694	1.3444	1.2194	0.25000	0.12500	0.12500	0.0927
1-3/4	4	1.7500	1.6250	1.5000	1.7169	1.5919	1.4669	0.25000	0.12500	0.12500	0.0927
2	4	2.0000	1.8750	1.7500	1.9646	1.8396	1.7146	0.25000	0.12500	0.12500	0.0927
2-1/4	3	2.2500	2.0833	1.9167	2.2125	2.0458	1.8792	0.33333	0.16667	0.16667	0.1236
2-1/2	3	2.5000	2.3333	2.1667	2.4605	2.2938	2.1272	0.33333	0.16667	0.16667	0.1236
2-3/4	3	2.7500	2.5833	2.4167	2.7085	2.5418	2.3752	0.33333	0.16667	0.16667	0.1236
3	2	3.0000	2.7500	2.5000	2.9567	2.7067	2.4567	0.50000	0.25000	0.25000	0.1853
4	2	4.0000	3.7500	3.5000	3.9500	3.7000	3.4500	0.50000	0.25000	0.25000	0.1853
5	2	5.000	4.7500	4.5000	4.9444	4.6944	4.4444	0.50000	0.25000	0.25000	0.1853

STUB ACME THREAD DIMENSIONS

Threads Per Inch	Pitch	Height of Thread	Total Thread Height	Thread Thickness	Crest of Internal Thread (basic)	Root of Internal Thread Frn=0.4224P
Threads Per Inch	P	h=0.3P	hs=ht	(basic), t=P/2	F=0.4224P	0.259 x allowance
16	0.06250	0.01875	0.0238	0.03125	0.0264	0.0238
14	0.07143	0.02143	0.0264	0.3571	0.0302	0.0276
12	0.08333	0.02500	0.0300	0.04167	0.0352	0.0326
10	0.10000	0.03000	0.0400	0.05000	0.0422	0.0370
9	0.11111	0.03333	0.0433	0.05556	0.0469	0.0417
8	0.12500	0.03750	0.0475	0.06250	0.0528	0.0476
7	0.14286	0.04285	0.0529	0.07143	0.0603	0.0551
6	0.16667	0.05000	0.0600	0.08333	0.0704	0.0652
5	0.20000	0.06000	0.0700	0.10000	0.0845	0.0793
4	0.25000	0.07500	0.0850	0.12500	0.1056	0.1004
3-1/2	0.28571	0.08571	0.0957	0.14286	0.1207	0.1155
3	0.33333	0.10000	0.1100	0.16667	0.1408	0.1356
2-1/2	0.40000	0.12000	0.1300	0.20000	0.1690	0.1638
2	0.50000	0.15000	0.1600	0.25000	0.2112	0.2060
1-1/2	0.66667	0.20000	0.2100	0.33333	0.2816	0.2764
1-1/3	0.75000	0.22500	0.2350	0.37500	0.3168	0.3116
1	1.00000	0.30000	0.3100	0.50000	0.4224	0.4172

FREQUENTLY ASKED QUESTIONS

What's the difference between Standard and Stub Acme threads?

Standard Acme threads have a full-depth 29° trapezoidal profile, giving maximum thread engagement and load capacity. Stub Acme threads use a shallower tooth height, useful where radial space is limited or where the mating part's wall thickness can't accommodate a full-depth thread, at the cost of reduced load capacity.

Why use an Acme thread instead of a standard screw thread?

Acme threads are designed for repeated linear motion and moderate side loading, such as in a lead screw or jack, where a standard 60° V-thread would wear or strip more quickly. The wider thread form also makes Acme threads easier to machine, especially in larger sizes.

Are Acme threads self-locking?

It depends on the lead angle and friction — many Acme lead screws are self-locking enough to hold a load in position without back-driving, particularly at lower lead angles, but this shouldn't be assumed without checking the specific thread's lead angle and the application's friction and safety requirements.

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