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BS 1580-1:2007:2009 Edition

BS 1580-1:2007:2009 Edition

$215.11

Unified screw threads – Screw threads with diameters ¼ in and larger. Requirements

Published By Publication Date Number of Pages
BSI 2009 118
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This part of BS 1580 specifies limits of sizes, and tolerances, for single-start, clearance-fit unified screw threads, in inch units, with nominal diameters in and above, having the ISO basic profile as specified in BS ISO 68‑2:1998.

The part of BS 1580 specifies the following unified thread series as follows:

  1. standard variable pitch series:

    • a coarse thread series (UNC) from in to 4 in nominal diameter;

    • a fine thread series (UNF) from in to in nominal diameter;

    • an extra fine thread series (UNEF) from in to in nominal diameter;

  2. standard constant pitch series:

    • a 4-threads per inch series (4 UN) from in to 6 in nominal diameter;

    • a 6-threads per inch series (6 UN) from in to 6 in nominal diameter;

    • an 8-threads per inch series (8 UN) from in to 6 in nominal diameter;

    • a 12-threads per inch series (12 UN) from in to 6 in nominal diameter;

    • a 16-threads per inch series (16 UN) from in to 6 in nominal diameter;

    • a 20-threads per inch series (20 UN) from in to 3 in nominal diameter;

    • a 28-threads per inch series (28 UN) from in to in nominal diameter;

    • a 32-threads per inch series (32 UN) from in to 1 in nominal diameter;

  3. a special thread series (UNS) with diameter/pitch combinations other than those specified for the standard series.

NOTE 1 A transition fit series and an interference fit series of UNC and UNF threads for application to screwed studs are given in BS 2693‑1 and -2, respectively.

NOTE 2 Bases of tolerances and allowances are given in Annex A, guidance for calculating limits of size is given in Annex B, information on crest forms of external threads is given in Annex C, some general symbols are given in Annex D (see 3.2), information on tolerances is given in Annex E, guidance on selection and use of the standard unified thread series is given in Annex F and information and guidance on tolerance classes is given in Annex G.

PDF Catalog

PDF Pages PDF Title
3 Contents
Section 1: General 1
1 Scope 1
2 Normative references 2
3 Terms and definitions and symbols 2
4 Profile of unified screw threads 3
Section 2: Standard series 9
5 Diameter/pitch combinations 9
6 Tolerance classes of external and internal threads 9
7 Limits of size, and tolerances, for uncoated threads 9
8 Allowances for uncoated threads 10
9 Coated threads 11
10 Gauges 14
11 Designation of unified screw threads 16
Section 3: Special series (UNS) 69
12 Diameter/pitch combinations, fractional sizes 69
13 Diameter/pitch combinations, decimal sizes 70
14 Tolerance classes of external and internal UNS threads 70
15 Tolerances and allowances 70
16 Coated UNS threads 71
17 Designation of UNS threads 71
Annexes
Annex A (informative) Bases of tolerances and allowances for unified screw threads in and larger 89
Annex B (informative) Outline guide, and examples, for calculating limits of size of untabulated UNS screw threads 95
Annex C (informative) Forms of the crest of external threads 101
Annex D (informative) General symbols 103
Annex E (informative) Tolerances on pitch and flank angle in relation to tolerance on effective diameter 106
Annex F (informative) Standard unified thread series, guidance on selection and use 108
Annex G (informative) Standard unified thread series, information and guidance regarding the tolerance classes 109
Bibliography 111
List of figures
Figure 1 – Basic profile of unified screw threads 5
Figure 2 – Design profiles of unified internal and external threads (maximum material condition) 6
Figure 3 – Limiting profiles for crests of external threads 8
Figure 4 – Classes of unified screw threads – Effective diameter tolerance zones of finished uncoated threads 12
Figure 5 – Classes of unified screw threads – Effective diameter tolerance zones of coated threads before and after coating 13
Figure 6 – Tolerance zones for unified threads, Class 1A external thread and Class 1B internal thread 14
Figure 7 – Tolerance zones for unified threads, Class 2A external thread and Class 2B internal thread 15
Figure 8 – Tolerance zones for unified threads, Class 3A external thread and Class 3B internal thread 16
4 Figure A.1 – Unified screw threads – Nomogram for effective (pitch) diameter tolerances, Class 2A 94
Figure C.1 – Crest profiles on external threads resulting from different production methods 102
Figure D.1 – General symbols 105
List of tables
Table 1 – Unified screw threads, standard series 20
Table 2 – Unified screw threads, standard series – Limits of size 22
Table 3 – Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – External threads Class 1A 48
Table 4 – Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – Internal threads Class 1B 49
Table 5 – Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – External threads Class 2A 50
Table 6 – Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – Internal threads Class 2B 51
Table 7 – Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – External threads Class 3A 52
Table 8 – Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – Internal threads Class 3B 53
Table 9 – Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – External threads Class 1A 54
Table 10 – Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – Internal threads Class 1B 54
Table 11 – Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – External threads Class 2A 55
Table 12 – Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – Internal threads Class 2B 55
Table 13 – Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – External threads Class 3A 56
Table 14 – Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – Internal threads Class 3B 56
Table 15 – Coarse thread series (UNC) – Basic dimensions 57
Table 16 – Fine thread series (UNF) – Basic dimensions 58
Table 17 – Extra fine thread series (UNEF) – Basic dimensions 59
Table 18 – 4-thread series (4 UN) – Basic dimensions 60
Table 19 – 6-thread series (6 UN) – Basic dimensions 61
Table 20 – 8-thread series (8 UN) – Basic dimensions 62
Table 21 – 12-thread series (12 UN) – Basic dimensions 63
Table 22 – 16-thread series (16 UN) – Basic dimensions 64
Table 23 – 20-thread series (20 UN) – Basic dimensions 65
Table 24 – 28-thread series (28 UN) – Basic dimensions 66
Table 25 – 32-thread series (32 UN) – Basic dimensions 67
Table 26 – Thread data for unified thread form 68
Table 27 – Diameter increments for UNS threads 69
Table 28 – Allowances for external threads of special diameter/pitch combinations (UNS threads) Classes 1A and 2A 72
Table 29 – Major diameter tolerances for external threads of special diameter/pitch combinations (UNS threads) 73
Table 30 – Effective and minor diameter tolerances for external threads of special diameter/pitch combinations (UNS threads) Class 1A 74
5 Table 31 – Effective and minor diameter tolerances for external threads of special diameter/pitch combinations (UNS threads) Class 2A 75
Table 32 – Effective and minor diameter tolerances for external threads of special diameter/pitch combinations (UNS threads) Class 3A 76
Table 33 – Effective diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads) Class 1B 77
Table 34 – Effective diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads) Class 2B 78
Table 35 – Effective diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads) Class 3B 79
Table 36 – Minor diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads) 80
Table 37 – Unified screw threads – Decimal inch diameters with preferred pitches 81
Table 38 – Limits of size for UNS threads having decimal inch basic sizes and preferred pitches 82
Table A.1 – Limits of size of unified threads as given by screw thread tolerance formulae 93
Table D.1 – General symbols 103
6 Foreword
7 Section 1: General
1 Scope
a) standard variable pitch series:
b) standard constant pitch series:
c) a special thread series (UNS) with diameter/pitch combinations other than those specified for the standard series.
8 2 Normative references
3 Terms and definitions and symbols
3.1 Terms and definitions
3.2 Symbols
9 4 Profile of unified screw threads
4.1 Basic profile
4.2 Design profiles
11 Figure 1 Basic profile of unified screw threads
12 Figure 2 Design profiles of unified internal and external threads (maximum material condition)
13 Figure 2 Design profiles of unified internal and external threads (maximum material condition) (continued)
14 Figure 3 Limiting profiles for crests of external threads
15 Section 2: Standard series
5 Diameter/pitch combinations
6 Tolerance classes of external and internal threads
a) external threads:
b) internal threads:
7 Limits of size, and tolerances, for uncoated threads
16 a) For UNC, UNF, 4 UN, 6 UN and 8 UN threads a length of engagement equal to one diameter has been used. These tolerances are re…
b) For UNEF, 12 UN, 16 UN, 20 UN, 28 UN, 32 UN and all UNS threads a length of engagement equal to 9P has been used. These tolerances are recommended for lengths of engagement between 5P and 15P.
8 Allowances for uncoated threads
17 9 Coated threads
a) Class 1A, external threads. The allowance shall be maintained after coating and the coated thread shall be accepted by the sa…
b) Class 2A, external threads. In the case of Class 2A coated threads, it shall be permissible for the allowance to be absorbed …
c) Class 2AG, external threads. Both the maximum and minimum diametral limits before coating shall be 0.001 in less than those given in Table 2 for Class 2A. After coating the maximum tabulated limits shall not be exceeded.
d) Class 3A, external threads. Since there is no allowance, the upper limits for all diameters of the thread before coating shal…
e) Internal threads (all classes). After coating, internal threads of all classes shall be accepted by a GO screw gauge of basic size. The upper limit shall not be changed.
18 Figure 4 Classes of unified screw threads – Effective diameter tolerance zones of finished uncoated threads
19 Figure 5 Classes of unified screw threads – Effective diameter tolerance zones of coated threads before and after coating
20 10 Gauges
Figure 6 Tolerance zones for unified threads, Class 1A external thread and Class 1B internal thread
21 Figure 7 Tolerance zones for unified threads, Class 2A external thread and Class 2B internal thread
22 Figure 8 Tolerance zones for unified threads, Class 3A external thread and Class 3B internal thread
11 Designation of unified screw threads
11.1 Basic designation
a) the nominal size (which is equal to the basic major diameter) expressed as a fraction or a decimal equivalent. (Where decimal equivalents are used they shall be shown in four-place decimals, but omitting the cipher in the fourth place.)
b) the number of threads per inch;
c) the thread series, UNC, UNF, UNEF or UN;
d) the thread class, 1A, 2A, 2AG, 3A, 1B, 2B or 3B.
23 11.2 Designation of coated threads
11.2.1 General
11.2.2 External threads
11.2.2.1 Class 1A threads
11.2.2.2 Class 2A threads
24 11.2.2.3 Class 2AG threads
11.2.2.4 Class 3A threads
11.2.3 Internal threads
25 11.3 Designation of left-hand threads
11.4 Designation of threads with a special length of engagement
11.5 Designation of threads with modified crests
26 11.6 Designation of threads with other alterations
Table 1 Unified screw threads, standard series
27 Table 1 Unified screw threads, standard series (continued)
28 Table 2 Unified screw threads, standard series – Limits of size
29 Table 2 Unified screw threads, standard series – Limits of size (continued)
30 Table 2 Unified screw threads, standard series – Limits of size (continued)
31 Table 2 Unified screw threads, standard series – Limits of size (continued)
32 Table 2 Unified screw threads, standard series – Limits of size (continued)
33 Table 2 Unified screw threads, standard series – Limits of size (continued)
34 Table 2 Unified screw threads, standard series – Limits of size (continued)
35 Table 2 Unified screw threads, standard series – Limits of size (continued)
36 Table 2 Unified screw threads, standard series – Limits of size (continued)
37 Table 2 Unified screw threads, standard series – Limits of size (continued)
38 Table 2 Unified screw threads, standard series – Limits of size (continued)
39 Table 2 Unified screw threads, standard series – Limits of size (continued)
40 Table 2 Unified screw threads, standard series – Limits of size (continued)
41 Table 2 Unified screw threads, standard series – Limits of size (continued)
42 Table 2 Unified screw threads, standard series – Limits of size (continued)
43 Table 2 Unified screw threads, standard series – Limits of size (continued)
44 Table 2 Unified screw threads, standard series – Limits of size (continued)
45 Table 2 Unified screw threads, standard series – Limits of size (continued)
46 Table 2 Unified screw threads, standard series – Limits of size (continued)
47 Table 2 Unified screw threads, standard series – Limits of size (continued)
48 Table 2 Unified screw threads, standard series – Limits of size (continued)
49 Table 2 Unified screw threads, standard series – Limits of size (continued)
50 Table 2 Unified screw threads, standard series – Limits of size (continued)
51 Table 2 Unified screw threads, standard series – Limits of size (continued)
52 Table 2 Unified screw threads, standard series – Limits of size (continued)
53 Table 2 Unified screw threads, standard series – Limits of size (continued)
54 Table 3 Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – External threads Class 1A
55 Table 4 Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – Internal threads Class 1B
56 Table 5 Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – External threads Class 2A
57 Table 6 Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – Internal threads Class 2B
58 Table 7 Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – External threads Class 3A
59 Table 8 Coarse thread series (UNC) – Limits and tolerances for finished uncoated threads – Internal threads Class 3B
60 Table 9 Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – External threads Class 1A
Table 10 Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – Internal threads Class 1B
61 Table 11 Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – External threads Class 2A
Table 12 Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – Internal threads Class 2B
62 Table 13 Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – External threads Class 3A
Table 14 Fine thread series (UNF) – Limits and tolerances for finished uncoated threads – Internal threads Class 3B
63 Table 15 Coarse thread series (UNC) – Basic dimensions
64 Table 16 Fine thread series (UNF) – Basic dimensions
65 Table 17 Extra fine thread series (UNEF) – Basic dimensions
66 Table 18 4-thread series (4 UN) – Basic dimensions
67 Table 19 6-thread series (6 UN) – Basic dimensions
68 Table 20 8-thread series (8 UN) – Basic dimensions
69 Table 21 12-thread series (12 UN) – Basic dimensions
70 Table 22 16-thread series (16 UN) – Basic dimensions
71 Table 23 20-thread series (20 UN) – Basic dimensions
72 Table 24 28-thread series (28 UN) – Basic dimensions
73 Table 25 32-thread series (32 UN) – Basic dimensions
74 Table 26 Thread data for unified thread form
75 Section 3: Special series (UNS)
12 Diameter/pitch combinations, fractional sizes
12.1 Diameters
Table 27 Diameter increments for UNS threads
12.2 Pitches
76 13 Diameter/pitch combinations, decimal sizes
a) Diameters shall be selected as follows.
2) Diameters above 6 in.
b) Pitches shall be selected from Table 1 or, where a pitch coarser than 4 t.p.i. is required, from Table 26.
14 Tolerance classes of external and internal UNS threads
15 Tolerances and allowances
77 16 Coated UNS threads
17 Designation of UNS threads
78 Table 28 Allowances for external threads of special diameter/pitch combinations (UNS threads) Classes 1A and 2A
79 Table 29 Major diameter tolerances for external threads of special diameter/pitch combinations (UNS threads)
80 Table 30 Effective and minor diameter tolerances for external threads of special diameter/pitch combinations (UNS threads) Class 1A
81 Table 31 Effective and minor diameter tolerances for external threads of special diameter/pitch combinations (UNS threads) Class 2A
82 Table 32 Effective and minor diameter tolerances for external threads of special diameter/pitch combinations (UNS threads) Class 3A
83 Table 33 Effective diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads) Class 1B
84 Table 34 Effective diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads) Class 2B
85 Table 35 Effective diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads) Class 3B
86 Table 36 Minor diameter tolerances for internal threads of special diameter/pitch combinations (UNS threads)
87 Table 37 Unified screw threads – Decimal inch diameters with preferred pitches
88 Table 38 Limits of size for UNS threads having decimal inch basic sizes and preferred pitches
89 Table 38 Limits of size for UNS threads having decimal inch basic sizes and preferred pitches (continued)
90 Table 38 Limits of size for UNS threads having decimal inch basic sizes and preferred pitches (continued)
91 Table 38 Limits of size for UNS threads having decimal inch basic sizes and preferred pitches (continued)
92 Table 38 Limits of size for UNS threads having decimal inch basic sizes and preferred pitches (continued)
93 Table 38 Limits of size for UNS threads having decimal inch basic sizes and preferred pitches (continued)
94 Table 38 Limits of size for UNS threads having decimal inch basic sizes and preferred pitches (concluded)
95 Annex A (informative) Bases of tolerances and allowances for unified screw threads in and larger
A.1 General
A.2 Tolerance classes
A.3 Allowances
A.4 Effective diameter tolerances
96 a) For UNC, UNF, 4 UN, 6 UN and 8 UN threads, a length of engagement equal to one diameter has been used.
b) For UNEF, 12 UN, 16 UN, 20 UN, 28 UN, 32 UN and all UNS threads, a length of engagement equal to 9P has been used.
A.5 Major diameter tolerances
A.5.1 External threads
A.5.2 Internal threads
A.6 Minor diameter tolerances
A.6.1 External threads
97 A.6.2 Internal threads
a) minimum tolerance 0.23P p 1.5P2 for 80 t.p.i. to 13 t.p.i. inclusive. [This corresponds to a minimum thread height of internal threads ranging from 67% for 80 t.p.i. to 74% for 13 t.p.i.(see Note).]
b) minimum tolerance 0.120P for 12 t.p.i. and coarser. [This corresponds to a minimum thread height of internal threads of 74% (see Note).]
98 A.7 Depth of thread engagement
100 Figure A.1 Unified screw threads – Nomogram for effective (pitch) diameter tolerances, Class 2A
101 Annex B (informative) Outline guide, and examples, for calculating limits of size of untabulated UNS screw threads
B.1 General
B.2 Uncoated external threads, Classes 1A, 2A and 3A
102 B.3 Uncoated internal threads, Classes 1B, 2B and 3B
B.4 Examples
107 Annex C (informative) Forms of the crest of external threads
a) Bolts with rounded crests are less susceptible than those having flat crests, to damage by burring during handling and transport, which results in sharp, or semi-sharp, edges round the outside diameter of the bolt.
b) Troubles associated with plating are far less serious if the crests of the bolts are rounded. In the plating of bolts by the …
c) The threads on thread-rolling dies are stronger, less subject to fatigue failure and easier to grind if their roots are rounded rather than sharp-cornered.
108 Figure C.1 Crest profiles on external threads resulting from different production methods
109 Annex D (informative) General symbols
Table D.1 General symbols
110 Table D.1 General symbols (continued)
111 Figure D.1 General symbols
112 Annex E (informative) Tolerances on pitch and flank angle in relation to tolerance on effective diameter
E.1 Effect of pitch errors
E.2 Effect of errors in flank angle
113 E.3 Criteria for acceptability of a combination of errors in the effective diameter, pitch and flank angle of a screw thread
a) External threads. The simple effective diameter of an external thread (as measured along the pitch line of the thread) should…
b) Internal threads. The simple effective diameter of an internal thread (as measured along the pitch line) should lie between t…
E.4 Tolerances on pitch and flank angle of a screw thread
114 Annex F (informative) Standard unified thread series, guidance on selection and use
F.1 General
F.2 Coarse thread series (UNC)
F.3 Fine thread series (UNF)
F.4 Extra fine thread series (UNEF)
115 F.5 Constant pitch series
a) 4-Thread series (4 UN). This series is intended for use where a very robust thread is needed.
b) 6-Thread series (6 UN). This series offers a robust thread which can be used for heavy duty applications where space is limited.
c) 8-Thread series (8 UN). This series, originally used for high-pressure joint bolts and nuts, is now widely used in the United…
d) 12-Thread series (12 UN). This series was originally devised for boiler practice to permit tapping out worn threads one size …
e) 16-Thread series (16 UN). This series gives a convenient and reasonably robust thread for use on large diameters in compact designs.
f) 20-Thread series (20 UN). This series provides a very convenient fine thread for compact designs of moderate diameter as the double depth of thread falls within in increments of basic size on diameter.
g) 28-Thread and 32-Thread series (28 UN and 32 UN). These series are intended for use on small to moderate diameters in designs for which the 20 UN series is too coarse.
Annex G (informative) Standard unified thread series, information and guidance regarding the tolerance classes
G.1 Classes 2A and 2B
116 G.2 Classes 3A and 3B
G.3 Classes 1A and 1B
117 Bibliography
BS 1580-1:2007
$215.11