BS-G-154-1958.pdf

BRITISH STANDARD OBSOLESCENT OCTOBER 1969 BS G 154:1958 Incorporating Amendment No. 1 (Replacing A.G.S. 1753 and 1754) Screws with captive washers for aircraft UDC 621.882.4:629.13 Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 This 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 31 December 1958 © BSI 03-2000 The following BSI references relate to the work on this standard: Committee reference ACE/6 Draft for comment CW (ACE) 9482 ISBN 0 580 34529 7 Foreword The screws and washers dealt with in this British Standard are used primarily in electrical connections. Although of slightly different dimensions, they are interchangeable with screws and washers complying with Ministry of Supply drawings A.G.S. 1753 and 1754, which the standard is intended to replace. A British Standard does 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 inside front cover, pages i to iv, pages 1 to 4 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 346October 1969 Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 © BSI 03-2000i Amendment Slip No.1 published 31 October, 1969 to British Standard G.154:1958 Screws with captive washers Obsolescence The need for this British Standard has been reviewed and it has been decided that, in view of the obsolescence of B.A. threads in accordance with BS 93 by Amendment No. 3 published in 1966 and adoption of Unified threads in modern aircraft, it should be regarded as obsolescent and not therefore used on new designs. It will be withdrawn in due course. In the meantime copies of the standard should be endorsed: OBSOLESCENT (See Amendment No. 1) Attention is drawn to British Standard G.203:1967, “Unified screws with captive facing and locking washers”. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 © BSI 03-2000iii Contents Page ForewordInside front cover 1Scope1 2Material1 3Dimensions1 4Ends of screws1 5Screw threads2 6Assembly2 7Finish2 8Freedom from defects before and after assembly3 9Identification3 Appendix Table for conversion of inches to approximate millimetre equivalents4 Figure 1 Types of end permissible on screws1 Figure 22 Figure 33 Table 1 Dimensions of screws2 Table 2 Nominal lengths and part numbers of screws3 Table 3 Dimensions and part numbers of washers3 Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 © BSI 03-20001 1 Scope This British Standard specifies the material, dimensions, finish and part numbers of B.A. screws with captive washers for use on aircraft. NOTEA table is given in the Appendix to provide a ready means of calculating the approximate millimetre equivalents of the inch dimensions. More accurate conversions should be based on the tables in BS 350. 2 Material The screws and washers shall be manufactured from mild steel having a tensile strength of not less than 25 tons/sq.in. (39 kg/mm2). 3 Dimensions a) The screws shall conform to the dimensions and tolerances given in Table 1 and Table 2. b) The washers shall conform to the dimensions given in Table 3. 4 Ends of screws a) Rolled threads. When screws are made with rolled threads the lead formed at the end of the screw by the thread-rolling operation may be regarded as providing the necessary chamfer to the end and no other machining operation is necessary, unless the purchaser, in his enquiry and order, has specified that the ends shall be finished as described in Clause 4 b), 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 with the gauge face. The distance between the gauge face and the high point of the screw end shall not exceed one pitch. b) Cut threads. The ends of screws with cut threads may, at the option of the manufacturer, 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 1: times the nominal diameter of the shank. NOTEFor convenience, one type of end only is illustrated in the figures at the head of Table 1. The three alternative types of end permissible are shown in Figure 1. Figure 1 Types of end permissible on screws Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 2 © BSI 03-2000 5 Screw threads a) The screw threads may be either cut or rolled at the option of the manufacturer. They shall conform, after plating, to the limits and tolerances specified for close class bolts, sizes 4 B.A. and 6 B.A., in BS 93, “British Association (B.A.) screw threads”. b) The minimum major, effective, and minor diameters of the threads before plating may be 0.25 mm (0.001 in.) smaller than the minimum dimensions specified in BS 93 in order to avoid any undue restriction of the tolerance allowed for screwing. c) The screw threads after plating shall pass gauges approved by the Inspecting Authority. 6 Assembly The washer shall be assembled on the screw in such a manner as to ensure that it is free to rotate on the unthreaded portion of the screw but will not pass over the thread. 7 Finish After assembly, the screws and washers shall be cadmium plated in accordance with the requirements of the latest issue of Ministry of Supply aircraft process specification D.T.D.904. Table 1 Dimensions of screws NOTEThe head diameter may be tapered as shown in Figure 2, or parallel to the axis of the screw. With the exception of the head taper, the head and slot dimensions conform to those for the relevant sizes of cheese head screws specified in Table 3 of BS A31-54, “British Association (B.A.) low tensile screws and nuts for aeronautical purposes.” Figure 2 For nominal lengths see Table 2 B.A. No. Major diameter of thread Diameter of plain portion of shank Minimum length of full form thread Length of plain portion of shank Diameter of head Depth of head Slot WidthDepth DUFLABHJ max.nom.max.min.max.min.min.max.nom. 6 B.A. in. 0.110 in. 0.095Nominal length of screw 0.05 in. in. 0.050 in. 0.194 in. 0.184 in. 0.078 in. 0.073 in. 0.027 in. 0.033 in. 0.035 4 B.A. 0.1420.125Nominal length of screw 0.055 in. 0.0550.252 0.242 0.101 0.095 0.034 0.040 0.045 Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 © BSI 03-20003 8 Freedom from defects before and after assembly a) The screw heads shall be concentric with the shank. Slots shall be clean and free from burrs and on visual inspection shall appear to be closely co-incident with the centre-line of the head. b) On visual inspection washers shall be flat and free from burrs and the hole shall be centrally located. c) Screws and washers may be rejected at any time for faults in, or revealed by, manufacture, although they have been made from material passed previously for chemical composition and mechanical properties. 9 Identification The screws and washers shall be identified for ordering purposes by the number of this British Standard and the appropriate part numbers shown in Table 2 and Table 3. For example, a 4 B.A. screw, 5/16in. long, with a size 5 washer will be BS G 154/B10/5. Table 2 Nominal lengths and part numbers of screws Table 3 Dimensions and part numbers of washers Length (inches) Part Number 6 B.A.4 B.A. 3/16 1/4 5/16 3/8 7/16 1/2 5/8 (0.188) (0.250) (0.313) (0.375) (0.438) (0.500) (0.625) A6 A8 A 10 A 12 A 14 A 16 B8 B 10 B 12 B 14 B 16 B 20 Figure 3 Part Number Dia. Ba ± 0.005 in. 1 2 3 4 5 6 7 in. 0.20 0.23 0.25 0.28 0.33 0.47 0.53 a Finished size after assembly on screw. Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 4 © BSI 03-2000 Appendix Table for conversion of inches to approximate millimetre equivalents Examples of use of table: 0.005 in. = 0.13 mm 0.53 in. = 12.7 + 0.762 = 13.5 mm InchesMillimetres 1 2 3 25.4 50.8 76.2 4 5 6 101.6 127.0 152.4 7 8 9 177.8 203.2 228.6 10254.0 Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank Licensed Copy: London South Bank University, London South Bank University, Sat Dec 09 03:12:00 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS G 154:1958 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British Standards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. 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