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1、BRITISH STANDARD BS A 31-54: 1951 Incorporating Amendment Nos. 1, 2, 3, 4 and 5 Specification for British Association (B.A.) low tensile screws and nuts for aeronautical purposes NOTEThe Institution desires to call attention to the fact that this standard is intended to include the technical provisi
2、ons necessary for the supply of the material herein referred to, but does not purport to comprise all the necessary provisions of a contract. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:1951 This
3、 British Standard, having been approved by the Aircraft Industry Standards Committee, and endorsed by the Chairman of the Engineering Divisional Council, was published under the authority of the General Council of the Institution on 30 March 1951 BSI 03-2000 ISBN 0 580 34558 0 A British Standard doe
4、s not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an insi
5、de front cover, pages i and ii, pages 1 to 9 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.Date of issueComments 1648
6、June 1953 2260August 1955 2412March 1956 3054May 1958 4065February 1961Indicated by a sideline in the margin Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:1951 BSI 03-2000i Contents Page 1Scope1 2M
7、aterial and manufacture1 2AFreedom from defects1 3Dimensions1 4Length of screws1 5Ends of screws1 6Screw threads1 7Length of thread on screws2 8Chamfering2 8ACountersinking2 9Finish2 10Identification2 Figure 1 Alternative types of ends permissible on screws2 Figure 24 Figure 35 Figure 46 Figure 57 F
8、igure 6 Hexagonal ordinary nut8 Figure 7 Hexagonal thin (or lock) nut8 Table 1 B.A. Screws British Standard numbers. Material and finish3 Table 2 B.A. Nuts British Standard numbers. Material and finish3 Table 3 Dimensions of cheese head screws4 Table 4 Dimensions of round head screws5 Table 5 Dimens
9、ions of countersunk head screws6 Table 6 Dimensions of raised-countersunk head screws7 Table 7 Dimensions of hexagonal ordinary (or full) nuts and thin (or lock) nuts8 Table 8 B.A. Screws Part numbers9 Table 9 B.A. Nuts Code letters9 Licensed Copy: London South Bank University, London South Bank Uni
10、versity, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:1951 BSI 03-20001 NOTEThe screws and nuts covered by these British Sta
11、ndards conform to the dimensions specified in BS 57:1951, “B.A. screws, bolts, nuts and plain washers”. The details given in Table 3 to Table 7 have been taken from that specification. 1 Scope These British Standards cover dimensions, material, finish and part numbers for British Association (B.A.)
12、cheese, round, countersunk, and raised-countersunk head screws, and dimensions, material, finish and code letters for British Association (B.A.) hexagon ordinary (or full) and thin (or lock) nuts for aeronautical use. 2 Material and manufacture The screws (turned from bar or cold forged) and nuts sh
13、all be manufactured from the appropriate material specified in Table 1 and Table 2 respectively. 2A Freedom from defects a) The screws and nuts shall be free from harmful defects. b) Screws and nuts may be rejected at any time for faults in, or revealed by, manufacture although they have been made f
14、rom material passed previously for chemical composition and mechanical tests. 3 Dimensions a) With the exception of the thread, the screws and nuts shall before coating conform to the dimensions and tolerances given in Table 3 to Table 6 for screws and Table 7 for nuts respectively. b) Screw heads s
15、hall be concentric with the shank. Slots shall be clean and free from burrs and, on visual inspection, shall appear to be closely coincident with the centre-line of the head. 4 Length of screws a) Cheese and round heads. The nominal length shall be the distance from the underside of the head to the
16、extreme end of the shank, including any chamfer or radius. b) Countersunk heads. The nominal length shall be the distance from the upper surface of the head to the extreme end of the shank, including any chamfer or radius. c) Raised-countersunk heads. The nominal length shall be the distance from th
17、e upper surface of the head (excluding the raised portion) to the extreme end of the shank, including any chamfer or radius. d) Tolerance on length. The permissible tolerance on the nominal length of screws shall be as follows: 5 Ends of screws (See Figure 1.) a) Cut threads. All screws with cut thr
18、eads shall be finished with either a flat chamfer with a 90 included angle to a depth slightly exceeding the depth of thread, or a radius approximately equal to 11/4 times the nominal diameter of the shank. b) Rolled threads. Screws with rolled threads need not be pointed, the lead formed during the
19、 thread rolling being sufficient, but the end shall be at right angles to the axis of the screw within the tolerance permitted by the following test: The screw shall be screwed into a ring gauge, the face of which is square to the axis of the thread, until the low point of the screw end is flush wit
20、h the gauge face. The distance between the gauge face and the high point of the screw end shall not exceed one pitch. 6 Screw threads a) Screws. i) The screw threads may be either cut or rolled at the option of the manufacturer. They shall conform (after coating, if required) to the limits and toler
21、ances specified for close class bolts in BS 93:1951 “British Association (B.A.) screw threads”. ii) The minimum major, effective, and minor diameters of threads of screws required to be coated may, before coating, be 0.001 in. smaller than the minimum dimensions specified in Table 8 of BS 93:1951, i
22、n order to avoid any undue restriction of the tolerance allowed for screwing. iii) In view of the tendency for closely fitting threads in stainless steel to seize when tightened together, the maximum major, effective and minor diameters of stainless steel screws shall be 0.001 in. below the maximum
23、specified in BS 93:1951, Table 8. The full close class tolerance specified in Table 8 of that standard shall, however, be allowed. b) Nuts. The screw threads shall conform to the limits and tolerances specified in BS 93:1951. They shall be required to pass gauges approved by the Inspecting Authority
24、. Nominal lengthTolerance Up to and including 1/8 in.+ 0.01 in. 0 Above 1/8 in. up to and including 1/2 in. + 0.02 in. 0 Above 1/2 in. + 1/32 in. 0 Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:195
25、1 2 BSI 03-2000 7 Length of thread on screws a) Cheese and round heads. These shall be threaded to leave a limited length of unthreaded shank under the head. The length of unthreaded shank is defined as the distance from the leading face of a nut which has been screwed as far as possible on to the s
26、crew by hand to the underside of the head. The nut shall have threads as specified in Clause 6 b) and shall not be countersunk. The length of unthreaded shank shall not exceed the following: b) Countersunk and raised-countersunk heads. These shall be threaded right up to the head. 8 Chamfering All n
27、uts shall have a chamfer of approximately 30 on both faces. 8A Countersinking All nuts shall be countersunk on one face to the major diameter of the thread at an angle of 90120, as indicated in Figure 6 and Figure 7. 9 Finish The screws and nuts shall conform to the finish for the appropriate materi
28、al specified in Table 1 and Table 2 respectively. 10 Identification The screws and nuts shall be identified for ordering purposes by the relevant British Standard number (see Table 1 and Table 2) and the appropriate part number (see Table 8) in the case of screws, or the appropriate code letter (see
29、 Table 9) in the case of nuts, e.g.: A countersunk head aluminium alloy 1/2 in. 4 B.A. screw is BS A 41 BS B 16. An aluminium alloy 4 B.A. ordinary nut is BS A 51 B. Figure 1 Alternative types of ends permissible on screws Nominal length of screw Length of unthreaded shank Up to and including 5 time
30、s the diameter Greater than 5 times the diameter Not to exceed 11/2 times the pitch. Not to exceed 21/2 times the pitch. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:1951 BSI 03-20003 Table 1 B.A.
31、 Screws British Standard numbers. Material and finish Table 2 B.A. Nuts British Standard numbers. Material and finish British Standard Type of head Material Finish Description Quality or specification Minimum tensile strength tons per sq. in. BS A 31 BS A 32 BS A 33 BS A 34 Cheese Round Countersunk
32、Raised countersunk Mild steelCommercial quality 25 Cadmium coated in accordance with latest issue of Ministry of Supply Aircraft Process Specification D.T.D. 904. BS A 35 BS A 36 BS A 37 BS A 38 Cheese Round Countersunk Raised countersunk Stainless steel BS 970, EN 56 series, EN 57, or EN 58 series
33、35Natural BS A 39 BS A 40 BS A 41 BS A 42 Cheese Round Countersunk Raised countersunk Aluminium alloy BS 1473, HB 15 WP NB 6 “ H BS 1476, HE 14 T HE 15 W or WP 20 Anodized in accordance with latest issue of Ministry of Supply Aircraft Process Specification D.T.D. 910. BS A 43 BS A 44 BS A 45 BS A 46
34、 Cheese Round Countersunk Raised countersunk BrassCommercial quality 20 Tin coated in accordance with latest issue of Ministry of Supply Aircraft Process Specification D.T.D. 924. British Standard Type of nut Material Finish Description Quality or specification Minimum tensile strength tons per sq.
35、in. BS A 47Ordinary Mild steelCommercial quality 25 Cadmium coated in accordance with latest issue of Ministry of Supply Aircraft Process Specification D.T.D. 904a. BS A 48Thin (or lock) BS A 49Ordinary Stainless steel BS 970, EN 56 series, EN 57, or EN 58 series 35Natural BS A 50Thin (or lock) BS A
36、 51Ordinary Aluminium alloy BS 1476, HE 14 T HE 15 W or WP 20 Anodized in accordance with latest issue of Ministry of Supply Aircraft Process Specification D.T.D. 910. BS A 52Thin (or lock) BS A 53Ordinary BrassCommercial quality20 Tin coated in accordance with latest issue of Ministry of Supply Air
37、craft Process Specification D.T.D. 924a. BS A 54Thin (or lock) a It is not necessary for the thread to be coated. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:1951 4 BSI 03-2000 Table 3 Dimensions
38、 of cheese head screws Figure 2 For nominal lengths see Table 8. 1234567891011 B.A. No. Diameter of shank and major diameter of thread Diameter of headaDepth of head Radius under head Slot WidthDepth DABRHJb max.max.min.max.min.max.max.min.nom. 2 mm. 4.7 in. 0.185 in. 0.319 in. 0.309 in. 0.130 in. 0
39、.123 in. 0.015 in. 0.052 in. 0.044 in. 0.058 43.60.1420.2520.2420.1010.0950.0100.0400.0340.045 62.80.1100.1940.1840.0780.0730.0100.0330.0270.035 82.20.0870.1570.1470.0630.0590.0100.0300.0240.027 101.70.0670.1120.1070.0450.0410.0070.0240.0190.020 121.30.0510.0950.0900.0380.0350.0050.0200.0150.017 a D
40、iameter of head. The dimensions specified for the diameter of head are based on the rule A = 1.75D, but they have been adjusted slightly to come within the dimensions of diameters of available round bars to British Standard limits. b Dimension J is measured from the upper surface of the head to the
41、point at which the slot breaks through. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:1951 BSI 03-20005 Table 4 Dimensions of round head screws Figure 3 For nominal lengths see Table 8. 12345678910
42、1112 B.A. No. Diameter of shank and major diameter of thread Diameter of heada Depth of head Radius under head Radius of head Slot WidthDepth DABRFHJb max.max.min.max.min.max.approx.max.min.nom. 2 mm. 4.7 in. 0.185 in. 0.319 in. 0.309 in. 0.130 in. 0.123 in. 0.015 in. 0.319 in. 0.052 in. 0.044 in. 0
43、.071 43.60.1420.2520.2420.1010.0950.0100.2520.0400.0340.056 62.80.1100.1940.1840.0780.0730.0100.1940.0330.0270.043 82.20.0870.1570.1470.0630.0590.0100.1570.0300.0240.035 101.70.0670.1120.1070.0450.0410.0070.1120.0240.0190.025 a 1. Diameter of head. The dimensions specified for the diameter of head a
44、re based on the rule A = 1.75D, but they have been adjusted slightly to come within the dimensions of diameters of available roundbars to British Standard limits. 2. Shape of head. The shape of the head shall closely approximate to a half-ellipse. Radius G (struck off the underside of the head) must
45、 pass through diameter A and touch radius F. b Dimension J is measured from the upper surface of the head to the point at which the slot breaks through. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-5
46、4:1951 6 BSI 03-2000 Table 5 Dimensions of countersunk head screws Figure 4 For nominal lengths see Table 8. 12345678910 B.A. No. Major diameter of thread Diameter of heada Depth of headSlot TotalWidthDepth DABEHJb max.max.min.nom.max.max.min.nom. 2 mm. 4.7 in. 0.185 in. 0.319 in. 0.309 in. 0.077 in
47、. 0.010 in. 0.052 in. 0.044 in. 0.036 43.60.1420.2520.2420.0650.0100.0400.0340.031 62.80.1100.1940.1840.0510.0090.0330.0270.024 82.20.0870.1570.1470.0430.0080.0300.0240.021 101.70.0070.1120.1070.0300.0070.0240.0190.016 121.30.0510.0950.0900.0280.0060.0200.0150.014 a Diameter of head. The dimensions
48、specified for the diameter of head are based on the rule A = 1.75D, but they have been adjusted slightly to come within the dimensions of diameters of available round bars to British Standard limits. b Dimension J is measured from the upper surface of the head to the point at which the slot breaks t
49、hrough. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:09:16 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS A 31-54:1951 BSI 03-20007 Table 6 Dimensions of raised-countersunk head screws Figure 5 For nominal lengths see Table 8. 123456789101112 B.A. No. Major diameter of thread Diameter of heada Depth of headSlot RadiusWidthDepth DAEBMFHJb max.max.min.max.nom.approx.nom.max.min.nom. 2 mm. 4.7 in. 0.185 in. 0.319 in. 0.309 in. 0.010 in. 0.077 in. 0.036 i
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