Unified Thread Standard

The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wide variety of other threaded fasteners used in these countries. It has the same 60° profile as the ISO metric screw thread, but the characteristic dimensions of each UTS thread (outer diameter and pitch) were chosen as an inch fraction rather than a millimeter value. The UTS is currently controlled by ASME/ANSI in the United States.

Origins

Basic profile

Each thread in the series is characterized by its major diameter D_maj and its pitch, P. UTS threads consist of a symmetric V-shaped thread. In any plane containing the thread axis, the flanks of the V have an angle of 60° to each other. The outermost 1⁄8 and the innermost 1⁄4 of the height H of the V-shape are cut off from the profile.

The major diameter D_maj is the diameter of the screw measured from the outer edge of the threads. The minor diameter D_min (also known as the root diameter) is the diameter of the screw measured from the inner edge of the threads. The major diameter may be slightly different from the shank diameter, which is the diameter of the unthreaded part of the screw. The diameters are sometimes given approximately in fractions of an inch (e.g. the major diameter of a #6 screw is 0.1380 in, approximately 9⁄64 in = 0.140625 in).

The pitch P is the distance between thread peaks. For UTS threads, which are single-start threads, it is equal to the lead, the axial distance that the screw advances during a 360° rotation. UTS threads do not usually use the pitch parameter; instead a parameter known as threads per inch (TPI) is used, which is the reciprocal of the pitch.

The relationship between the height H and the pitch P is found using the following equation where $\theta$ is half the included angle of the thread, in this case 30 degrees:^[1]

H={\frac {1}{2\tan \theta }}\cdot P={\frac {\sqrt {3}}{2}}\cdot P\approx 0.866025\cdot P

or

P=2\tan \theta \cdot H={\frac {2}{\sqrt {3}}}\cdot H\approx 1.154701\cdot H.

In an external (male) thread (e.g., on a bolt), the major diameter D_maj and the minor diameter D_min define maximum dimensions of the thread. This means that the external thread must end flat at D_maj, but can be rounded out below the minor diameter D_min. Conversely, in an internal (female) thread (e.g., in a nut), the major and minor diameters are minimum dimensions, therefore the thread profile must end flat at D_min but may be rounded out beyond D_maj. These provisions are to prevent any interferences.

The minor diameter D_min and effective pitch diameter D_p are derived from the major diameter and pitch as:

{\begin{aligned}D_{\text{min}}&=D_{\text{maj}}-2\cdot {\frac {5}{8}}\cdot H=D_{\text{maj}}-{\frac {5{\sqrt {3}}}{8}}\cdot P\approx D_{\text{maj}}-1.082532\cdot P\\D_{\text{p}}&=D_{\text{maj}}-2\cdot {\frac {3}{8}}\cdot H=D_{\text{maj}}-{\frac {3{\sqrt {3}}}{8}}\cdot P\approx D_{\text{maj}}-0.649519\cdot P.\end{aligned}}

Designation

The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch. For diameters smaller than 1/4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.

This number pair is optionally followed by the letters UNC, UNF or UNEF (Unified) if the diameter-pitch combination is from the coarse, fine, or extra fine series, and may also be followed by a tolerance class.

Example: #6-32 UNC 2B (major diameter: 0.1380 inch, pitch: 32 tpi)

Zdroj:https://en.wikipedia.org?pojem=Unified_Thread_Standard
Text je dostupný za podmienok Creative Commons Attribution/Share-Alike License 3.0 Unported; prípadne za ďalších podmienok. Podrobnejšie informácie nájdete na stránke Podmienky použitia.

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Text je dostupný za podmienok Creative Commons Attribution/Share-Alike License 3.0 Unported; prípadne za ďalších podmienok.
Podrobnejšie informácie nájdete na stránke Podmienky použitia.

Unified Screw Threads — UNC, UNF and UNEF^[2]^: 1816
Major diameter D_maj (inch, mm)			Thread density (d, threads per inch) and thread pitch (p)									Preferred cutting tap drill size
			Coarse (UNC)			Fine (UNF)			Extra fine (UNEF)			Preferred cutting tap drill size
			d (TPI)	p (inch, mm)		d (TPI)	p (inch, mm)		d (TPI)	p (inch, mm)		Coarse		Fine		Extra fine
#0	0.0600	1.5240	None			80	0.012500	0.3175	None					3/64″	.047
#1	0.0730	1.8542	64	0.015625	0.3969	72	0.013888	0.3528	None			#53	.060	#53	.060
#2	0.0860	2.1844	56	0.017857	0.4536	64	0.015625	0.3969	None			#50	.070	#50	.070
#3	0.0990	2.5146	48	0.020833	0.5292	56	0.017857	0.4536	None			#47	.079	#45	.082
#4	0.1120	2.8448	40	0.025000	0.6350	48	0.020833	0.5292	None			#43	.089	#42	.094
#5	0.1250	3.1750	40	0.025000	0.6350	44	0.022727	0.5773	None			#38	.102	#37	.104
#6	0.1380	3.5052	32	0.031250	0.7938	40	0.025000	0.6350	None			#36	.107	#33	.113
#8	0.1640	4.1656	32	0.031250	0.7938	36	0.027778	0.7056	None			#29	.136	#29	.136
#10	0.1900	4.8260	24	0.041667	1.0583	32	0.031250	0.7938	None			#25	.150	#21	.159
#12	0.2160	5.4864	24	0.041667	1.0583	28	0.035714	0.9071	32	0.031250	0.7938	#16	.177	#14	.182	3/16″	.188
1/4″	0.2500	6.3500	20	0.050000	1.2700	28	0.035714	0.9071	32	0.031250	0.7938	#7	.201	#3	.213	7/32″	.219
5/16″	0.3125	7.9375	18	0.055556	1.4111	24	0.041667	1.0583	32	0.031250	0.7938	F	.257	I	.272	9/32″	.281
3/8″	0.3750	9.5250	16	0.062500	1.5875	24	0.041667	1.0583	32	0.031250	0.7938	5/16″	.313	Q	.332	11/32″	.344
7/16″	0.4375	11.1125	14	0.071428	1.8143	20	0.050000	1.2700	28	0.035714	0.9071	U	.368	25/64″	.391	Y	.404
1/2″	0.5000	12.7000	13	0.076923	1.9538	20	0.050000	1.2700	28	0.035714	0.9071	27/64″	.422	29/64″	.453	15/32″	.469
9/16″	0.5625	14.2875	12	0.083333	2.1167	18	0.055556	1.4111	24	0.041667	1.0583	31/64″	.484	1/2″	.500	+33/64″	.516
5/8″	0.6250	15.8750	11	0.090909	2.3091	18	0.055556	1.4111	24	0.041667	1.0583	+17/32″	.531	+9/16″	.563	+37/64″	.578
3/4″	0.7500	19.0500	10	0.100000	2.5400	16	0.062500	1.5875	20	0.050000	1.2700	21/32″	.656	11/16″	.688	+45/64″	.703
7/8″	0.8750	22.2250	9	0.111111	2.8222	14	0.071428	1.8143	20	0.050000	1.2700	+49/64″	.766	+51/64″	.797	+53/64″	.828
1″	1.0000	25.4000	8	0.125000	3.1750	12^[a]	0.083333	2.1167	20	0.050000	1.2700	7/8″	.875	59/64″	.922	61/64″	.953
1+1/8″	1.1250	28.5750	7	0.142857	3.6286	12	0.083333	2.1167

[1]

[2]

[a]