1、BRITISH STANDARD AEROSPACE SERIES BSG203:1967 Specification for Unified screws with captive facing and locking washers UDC 629.7:621.882.2.082.3:621.882.4/.5BSG203:1967 This BritishStandard, having been approved by the Aerospace Industry Standards Committee and endorsed by the Chairman ofthe Enginee
2、ring Divisional Council, was published under theauthority of the General Council of the Institution on 20November1967 BSI 02-2000 The following BSI references relate to the work on this standard: Committee reference ACE/14 Draft for comment D65/8950 ISBN 0 580 34545 9 Foreword The screws with captiv
3、e facing and locking washers dealt with in this BritishStandard are intended for use primarily for connecting electrical terminals to equipment. This BritishStandard which lists stainless steel screws with Unified threads, is intended for new applications and will replace BSG154 which lists mild ste
4、el screws with B.A. threads. The single captive load-bearing washer specified in BSG154 is replaced in this standard by captive load-bearing and locking washers. Only one length of screw is specified, catering for either one or two terminal ends to BSG204* The overall dimensions of the screws are si
5、milar to corresponding screws in the American National Aircraft Standard720 (NAS720) but the dimensions of the locking washers conform to the appropriate BritishStandard. This standard makes reference to the following BritishStandards: BS970, Wrought steels in the form of bars, billets and forgings,
6、 up to6in ruling section, for automobile and general engineering purposes. EN series. BS1449, Steel plate, sheet and strip. BS1580, Unified screw threads Part3: Diameters below: in. BSSP47, Single coil spring washers for aircraft. BSG204, Copper terminal ends for crimping to electric cables with cop
7、per conductors. NOTEThe figures in British units are to be regarded as the standard. A table is given inAppendix A to provide a ready means of calculating the approximate metric equivalents. More accurate conversions should be based on the tables in BS350, “Conversion factors and tables”. A British
8、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 co
9、ver, an inside front cover, pagesi andii, pages1 and 2, an inside back cover 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 Am
10、d. No. Date CommentsBSG203:1967 BSI 02-2000 i Contents Page Foreword Inside front cover 1 Scope 1 2 Materials and finishes 1 3 Screw threads 1 4 Dimensions 1 5 Ends of screws 1 6 Assembly 1 7 Identification and marking 1 Appendix A Table for conversion of inches to millimetre equivalents Inside back
11、 cover Figure1 2 Table 1 Dimensions of unified screws with captive facing and lockingwashers for aircraft 2ii blankBSG203:1967 BSI 02-2000 1 1 Scope This BritishStandard specifies the dimensions, materials, finishes and thread form of screws with captive and locking washers. The standard is restrict
12、ed to three sizes of screws commonly used with electrical terminations and to single-turn locking washers. Further types of locking washers may be included at a later date. 2 Materials and finishes 2.1 The screws shall be of austenitic stainless steel to BS970 EN58 series. 2.2 The facing washers sha
13、ll be of stainless steel complying with BS1449, EN58 series. 2.3 The locking washers shall be cadmium plated steel, single-coil spring washers, compying with BSSP47. 3 Screw threads The screw threads shall be rolled. They shall be Unified threads of the form specified in BS1580-3, and shall conform
14、to the Class2A form limits and tolerances therein. 4 Dimensions The assembled screw with locking-washer and facing washer shall conform to the dimensions shown inTable 1. The internal diameter of the facing washer shall be such that, when assembled, the requirements of6.1 are met. 5 Ends of screws T
15、he 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. The end shall be at right angles to the axis of the screw within the tolerance permitted by the following test: The scre
16、w 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. 6 Assembly 6.1 The washers shall be asse
17、mbled on the screws in such a manner as to ensure that they are free to rotate on the unthreaded portion of the screw, but the facing washer shall not engage with or pass over the thread. 6.2 The screw heads shall be concentric with the shank. Slots shall be clean and free from burrs and on visual i
18、nspection shall appear to be closely co-incident with the centre-line of the head. 6.3 On visual inspection, washers shall be flat and free from burrs, and the hole shall be centrally located. 6.4 Screws and washers may be rejected at any time for faults in, or revealed by, manufacture although they
19、 have been made from material passed previously for chemical composition and mechanical properties. 7 Identification and marking 7.1 The screws shall be made into parcels bearing the number of this BritishStandard and the appropriate code letter (seeTable 1). 7.2 The screws shall be identified for o
20、rdering purposes by the number of this BritishStandard and the appropriate code letter. For example, a No.6 UNC screw is BSG203/B. BS G 203:1967 2 BSI 02-2000 Table 1 Dimensions of unified screws with captive facing and locking washers for aircraft Figure 1 Third angle projection All dimensions are
21、in inches Size of screw Code letter Basic thread diameter D A E F H J L M N R S(ref) T U max. min. max. min. max. min. max. min. max. min. max. min. max. min. nom. nom. max. max. min. max. min. 440 UNC A 0.112 0.219 0.205 0.123 0.118 0.095 0.065 0.068 0.058 0.039 0.031 0.562 0.530 0.245 0.225 0.032
22、(21 SWG) 0.042 0.244 0.040 0.030 0.015 0.005 632 UNC B 0.138 0.270 0.256 0.131 0.126 0.117 0.085 0.082 0.072 0.048 0.039 0.562 0.530 0.320 0.310 0.040 (19 SWG) 0.046 0.310 0.050 0.037 0.015 0.005 1032 UNF D 0.190 0.373 0.357 0.167 0.162 0.167 0.135 0.110 0.099 0.060 0.050 0.562 0.530 0.410 0.400 0.0
23、40 (19 SWG) 0.061 0.399 0.068 0.053 0.020 0.010BSG203:1967 BSI 02-2000 Appendix A Table for conversion of inches to millimetre equivalents in mm 1 2 3 4 5 6 7 8 9 10 25.4 50.8 76.2 101.6 127.0 152.4 177.8 203.2 228.6 254.0 Example of use of table: 1 9 / 16 in=1.56in=25.4+12.7+1.524=39.6mm 0.875in 20
24、.32+1.778+0.127=22.2mm These examples give arithmetic conversions. For conversion to the required accuracy to ensure dimensional interchangeability, use BS 2856, “Precise conversion of inch and metric sizes on engineering drawings”.BSG203:1967 BSI 389 Chiswick High Road London W4 4AL BSIBritishStand
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