1、BSI BSXLSBL O1 = 1b24bbS 0334251 345 M _/ - BRITISH STANDARD Specification for Unified machine screws and machine screw nuts BS 1981 : 1991 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Policy C
2、oimittee (GME/-) to Ichnical Committee GME/9, upon which the following bodies were represented: BEAMA Ltd. British Constructional Steelwork Association Ltd. British Industrial Fsteners Federation British Railways Board British Steel Industry British Steel Industry (Wire Section) Gauge and bol Makers
3、 Association Ministry of Defence Society of Motor Manufacturers and Traders Limited Washer Manufacturers Association of Great Britain The foliowing bodies were also represented in the drafting of the standard, through subcommittees and panels: This British Standard, having been prepared under the di
4、rection of the General hlechanical Engineering Standards Policy Committee, was published under the authority of the Standards oard and comes into effect on 30 August 1991 o RSI 1991 “lie following MI references relat.e to the work on this Standard: Corninittee reference GMEIS Draft for comment 89179
5、991 DC ISBN O 580 19530 9 British Furniture Manufacturers Fedemtion British Independent Steel Producers Association National Association of Wtener Stockholders Amendments issued since publication BSI BS*19B1 O1 H 1624669 0334253 118 H BS 1981 : 1991 Contents we Committees responsible Inside front co
6、ver Foreword 4 Specification 1 Scope 5 2 rminology 5 3 Material 5 4 General dimensions 5 5 Heads of screws 5 6 Screw threads 6 7 Nominal length of screws 6 8 Length of thread on screws 6 9 Diameter of unthreaded shank on screws 7 10 Radius under the head of screws 7 11 Ends of screws 7 12 Designatio
7、n 9 Appendices A Dimensions of 80 countersunk head screws 33 B Standard sizes of machine screws 34 C Metric slot widths 39 Ibles 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Under head radii Header point dimensions for UNC screws Header point dimensions for UNF screws Slotted countersunk head machine screws Rec
8、essed countersunk head machine screws: details of recess type Z Slotted truncated countersunk head machine screws: short length Recessed truncated countersunk head machine screws: details of recess type Z Slotted raised countersunk head machine screws Recessed raised countersunk head machine screws:
9、 details of recess type z Slotted truncated raised countersunk head machine screws: short length Recessed truncated raised countersunk head machine screws: details of recess type Z Slotted and recessed pan head machine screws Recessed pan head machine screws: details of recess type Z Slotted raised
10、cheese head machine screws 8 9 9 10 11 12 13 14 15 16 17 18 19 20 - 1 BS 1981 : 1991 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Recessed raised cheese head machine screws: details of recess type Z Plain and slotted hexagon head machine screws Symmetry and concentricity tolerances Nominal
11、lengths and tolerances for machine screws Dimensions of machine screw nuts: precision type sizes No. O to No. 12 Dimensions of machine screw nuts: pressed type, square and hexagon Recessed countersunk head machine screws: details of recess type V Recessed truncated counteisunk head machine screws: d
12、etails of recess type V Recessed raised counteisunk head machine screws: details of recess type v Recessed truncated raised contersunk head machine screws: details of recess type V Recessed pan head machine screws: details of recess type V Recessed raised cheese head machine screws: details of reces
13、s type V Standard sizes for countersunk head machine screws: IS0 inch (Unified) threads Standard sizes for raised counteisunk head machine screws: IS0 inch (Unified) threads Standard sizes for pan head machine screws: IS0 inch (Unified) threads Standard sizes for raised cheese head machine screws: I
14、S0 inch (Unified) threads Standard sizes for hexagon head machine screws: IS0 inch (Unified) threads Metric slot widths Page 21 22 23 24 25 26 27 28 29 30 31 32 34 35 36 37 38 39 Figures 1 2 3 4 5 6 7 8 9 10 11 Rolled thread end Cut. thread chamfered end Cut thread radiused end Cone pointed ends Hea
15、der point Slotted counteisunk head niachino screws Recessed countersunk head machine screws: enlarged views of recess type Slotted truncated counteisunk head machine screws Recessed truncated countersunk head machine screws: enlarged views of recess type 2 Slotted raised counteisunk head machine scr
16、ews Recessed raised countersunk head machine screws: enlarged views of recess type 2 7 7 7 8 8 10 11 12 13 14 15 BSI BS*198L 01 = Lb24669 0334255 T0 - - BS 1981 : 1991 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Slotted truncated countersunk head machine screws Recessed truncated raised co
17、untersunk head machine screws: enlarged views of recess type Z Slotted and recessed pan head machine screws Recessed pan head machine screws: enlarged views of recess type Z Slotted raised cheese head machine screws Recessed raised cheese head machine screws: enlarged views of recess type Z Plain an
18、d slotted hexagon head machine screws Symmetry and concentricity tolerances Machine screw nuts: precision type, sizes No. O to No. 12 Machine screw nuts: pressed type Recessed countersunk head machine screws: enlarged views of recess type v Recessed truncated countersunk head machine screws: enlarge
19、d views of recess type V Recessed raised countersunk head machine screws: enlarged views of recess type V Recessed truncated raised countersunk head machine screws: enlarged views of recess type V Recessed pan head machine screws: enlarged views of recess type V Recessed raised cheese head machine s
20、crews: enlarged views of recess type V Size of countersunk screw head Edge of head of countersunk screw Page 16 17 18 19 20 21 22 23 25 26 27 28 29 30 31 32 33 33 BS 1981 : 1991 Foreword This British Standard lias been prepared under the direction of the General Mechanical Engineering Standards Poli
21、cy Committee. This revision of the standard supersedes BS 1981 : 1972 which is withdrawn. The principal changes that have been made in this edition are as follows. (a) The single recess type in the previous edition is now nominated as type Z and recess depth data have been deleted. Penetration value
22、s for cross recesses are now required to comply with BS 6605 : 1990. (b) New requirements for recess type V have been added. Penetration values for this type are also required to comply with BS 6605, Promt ce.r(j?katzon. Users of this British Standard are advised to consider the desirability of thir
23、d party certification of product conformity with this British Standard based on testing and continuing surveillance, which may be coupled with assessment of a suppliers quality systems against the appropriate Part of BS 5750. Enquiries as to the availability of third party certification schemes wiil
24、 be forwarded by BSI to the Association of Certification Bodies. If a third party certification scheme does not already exist, useis should consider approaching an appropriate body froin the list of Association members. Compliance with a British Standard does not of itself confer immunity from legal
25、 obligations. 4 BSI BS%LSBL 0% m Lb24bb 0334257 Bb3 m _- - BS 1981 : 1991 Specification 1 Scope This British Standard specifies requirements for the dimensions, tolerances and mechanical properties of machine screws and machine screw nuts having IS0 inch (Unified) screw threads. Dimensions and toler
26、ances are given for machine screws and nuts in the following diameter ranges: (a) hexagon head machine screws from No. 2 to No. 12; (b) slotted countersunk and pan head machine screws from No. O to i in; (c) slotted raised cheese head machine screws (non-preferred) from No. O to f in; (d) slotted ra
27、ised countersunk machine screws from No. O to i in; (e) slotted hexagon head machine screws (non-preferred) No. 4 to 12; (f) recessed (types Z and V) pan and countersunk head machine screws from No. 2 to i in; (g) recessed (types Z and V) raised cheese head machine screws (non-preferred) from No. 2
28、to (h) recessed (types Z and V) raised countersunk head machine screws from No. 2 to i in; ; in; (i) square and hexagon machine screw nuts, pressed type, from No. O to i in; (j) hexagon machine screw nuts, precision type, from No. O to No. 12. Mechanical properties are specified for steel, brass and
29、 aluminium alloy machine screws and machine screw nuts. Appendices are included that relate to the dimensioning of 80 countersunk heads, slot widths and standard sizes (not to be confused with stock sizes, see note 1 to table 27). NOTE 1. Attention is drawn to the fact that it is claimed that the ty
30、pe V recess is the subject of British patent no. 1 521 141 copies of which can be obtained from the Patent Office, 25 Southampton Buildings, London WC2A 1AY. BSI takes no position as to the validity of the patent or whether it is still in force. The patent is irrevocably endorsed licences of right u
31、nder Section 46 of the Patents Act 1977, which states: (3) Where such an entry is made in respect of a patent - (a) any person shall, at any time after the entry is made, be entitled as of right to a licence under the patent on such terms as may be settled by agreement or, in default of agreement, b
32、y the Comptroller on the application of the proprietor of the patent or the person requiring the licence. Licence details may be obtained from the registered proprietor of the patent. NCYE 2. Details of precision hexagon screws and nuts i in diameter and above are given in BS 1768. NOTE 3. The title
33、s of the British Standards referred to in this standard are iisted on the inside back cover. 2 Terminology 2.1 For the purposes of this British Standard the generic term screws has been adopted as applying to the products whether threaded up to the head or having an unthreaded portion of shank. 2.2
34、The designations of the various types of screw and nut are in accordance with those commonly used in the United Kingdom. 3 Material The material from which the screws and nuts are manufactured shall have a tensile strength not less than the following: steel 25 tonf/in2 (386 MPa) brass 20 tonf/in2 (3
35、09 MPa) aluminium alloy 20 tonf/in2 (309 Mpa) NOTE 1. These minimm tensile strengths may be taken as applicable to the finished products. NUE 2. Screws and nuts that comply with the requirements of this standard are not normaiiy subjected to test, but where this is required the purchaser is to state
36、 so in his enquiry and order. NUE 3. if the purchaser quires screws and nuts to be manufactured from steel of a higher tensile strength, or from another material, this is to be subject to agreement between the purchaser and the supplier. 4 General dimensions 4.1 Screws The general dimensions and tol
37、erances for screws shall be as given in tables 1 to 18 inclusive, clauses 6 to 12 inclusive and tables 21 to 26 inclusive. 4.2 Precision nuts (normal applications) The general dimensions and tolerances for nuts shall be as given in table 19 and in 6.3. 4.3 Pressed nuts (light duty applications) The
38、general dimensions and tolerances for pressed nuts shall be as given in table 20 and in 6.4. 5 Heads of screws 5.1 The screw heads shall be concentric with the shank within the tolerances given in table 17, using the head diameter or across flats dimension as datum. 5.2 The slots and recesses shall
39、be clean and free from burrs and shall be symmetrical with the shank within the tolerances given in table 17, using the shank diameter as datum. BS 1981 : 1991 5.3 The depth of slot (t) shall be measured from the top of the head to the point at which the slot breaks through the side. 5.4 The depth o
40、f the recess shail be such that, when measured in accordance with BS 6605, the penetration of the gauge into the recess complies with the penetration values given in tables 5, 7, 9, Il, 13, 15 and 21 to 26 inclusive. 5.5 The bearing surface of perpendicular bearing surface screw heads shall be at ri
41、ght angles to the axis of the body within 2O. 5.6 The taper of sides of hexagon head screws (see table 16), i.e. the angle between one side and the axis, shall not exceed 2O or 0.004 in, whichever is the greater. The specified limits across flats shall relate to the larger end of taper. Where edges
42、and corners of hexagon surface or upset type hexagon heads are slightly rounded, the diameter of the bearing surface shall be not less than 90 % of the minimum across flats dimensions. NOIX. The head height indicated in the dimensional tables represents a metal to metal measurement, i.e. on heads ha
43、ving rounded top surfaces the truncation of the rounded surface due to slot or recess is not considered part of the head height. 6 Screw threads . 6.1 General The screw threads shall be IS0 inch (Unified) series threads complying with BS 1680 : Parts 1 pitches for truncated countersunk and truncated
44、 raised countersunk heads and two pitches for all other head styles. NOTE. The length of unthreaded shank is defined as the distance from the leading face of a nut that has been screwed as far as posible onto the screw by hand up to: (a) the junction of the basic major diameter and the countersunk p
45、ortion of the head on countersunk and iaiscd countersunk heads; or (b) the iindrrside of the head on all other types of head. 6 BSI BS*L98L 01 m Lb24669 0334259 636 m . _- BS 1981 : 1991 9 Diameter of unthreaded shank on screws The diameter of the unthreaded portion of the shank on screws shall be n
46、ot greater than the basic major diameter of the screw thread and shall be not less than the minimum effective diameter of the screw thread. NOTE 1. Where it is essential that the diameter of the unthreaded portion of the shank shaii be not less than the minimum major diameter of the thread this shou
47、ld be stated by the purchaser. NOTE 2. The diameter of the unthreaded portion of shank is closely associated with the method of manufacture. It wiU generally be nearer the major diameter of the thread for turned screws and nearer the effective diameter for those produced by cold heading. 10 Radius u
48、nder the head of screws 10.1 Screws having heads with perpendicular bearing surface, e.g. pan, hexagon, raised cheese, truncated countersunk and truncated raised countersunk shall have a radius or fiilet radius running smoothly into the face of the head and shank without any step or discontinuity. T
49、he minimum and maximum radii shall be in accordance with those given in table 1. NOTE. The maximum values of radius are based upon 15 % of the basic screw diameter. 10.2 Countersunk and raised countersunk head screws shall have a radius running smoothly into the conical bearing surface of the head and the shank without any step or discontinuity. The minimum and maximum radii shall be in accordance with those given in table 1. NOTE. The maximum values of radius are based upon 40 % of the basic screw diameter. 10.3 All radii for flat and conical bearing shall be m
