1、BSI Standards PublicationBS A 401-420:2015AEROSPACE SERIESSpecification for screws, panand 100 countersunk head,hexalobular drive recess(unified threads below14inch) in various materialsPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the documen
2、twas last issued. The British Standards Institution 2015Published by BSI Standards Limited 2015ISBN 978 0 580 82769 3ICS 49.030.20The following BSI references relate to the work on this document:Committee reference ACE/12Draft for comment 15/30281806DCPublication historyFirst published October 2015A
3、mendments issued since publicationDate Text affectedBS A 401-420:2015 BRITISH STANDARDContents1 Scope 12 Normative references 13 General 24 Quality assurance procedure 25 Material and manufacture 36 Protective finish 37 Freedom from defects 38 Dimensions 39 Head of screws 410 Hexalobular drive reces
4、s 811 Unified thread identifier 1012 Length of screws 1213 Screw threads 1514 Ends of screws 1515 Length of thread 1616 Designation 1717 Identification and marking 17AnnexesAnnex A (informative) Screw equivalency quick reference guide 19Annex B (informative) Conversion tables 20Annex C (informative)
5、 Measuring inspection criteria for countersunk heads 21Annex D (informative) Derivation of design of the countersunk head 24Bibliography 27List of figuresFigure 1 Hexalobular recess in 100 countersunk heads 8Figure 2 Hexalobular recess in pan heads 9Figure 3 Unified thread identifier option 1 (annul
6、ar groove) 11Figure 4 Unified thread identifier option 2 (plain cylindrical extension) 11Figure 5 Dimensions of countersunk head screws 13Figure 6 Dimensions of pan head screws 14Figure7Types of end permissible on screws 16Figure C.1 Method of measuring head protrusion of countersunk headscrews 21Fi
7、gure C.2 Typical gauge block for 100 countersunk head screws 22Figure D.1 Formulae for dimensions for countersunk head screws 24Figure D.2 Absolute max and min head conditions of countersunk headscrews 26List of tablesTable 1 Sampling plan 3Table 2 British Standard identifier, material and finish of
8、 screws 5Table 3 Dimensions of hexalobular recesses for 100 countersunk heads 9Table 4 Dimensions of hexalobular recesses for pan heads 10Table 5 Unified thread identifier option 2 12Table 6 Dimensions of countersunk head screws 13Table 7 Dimensions of pan head screws 14Table8Tolerance on length 15T
9、able 9 Nominal length and part number codes 17Table A.1 Recess screw comparison to slotted screw equivalent 19Table B.1 Shank gauge and inch decimal to millimetre equivalents of basicdiameters of screws 20BRITISH STANDARD BS A 401-420:2015 The British Standards Institution 2015 iTable C.1 Dimensions
10、 of gauge block for 100 countersunk head screws 23Summary of pagesThis document comprises a front cover, an inside front cover, pages i to iv,pages 1 to 28, an inside back cover and a back cover.BRITISH STANDARDBS A 401-420:2015ii The British Standards Institution 2015ForewordPublishing informationT
11、his British Standard is published by BSI Standards Limited, under licence from The British Standards Institution, and came into effect on 31 October 2015. It was prepared by Technical Committee ACE/12, Aerospace fasteners and fastening systems. A list of organizations represented on this committee c
12、an be obtained on request to its secretary.Information about this documentThis British Standard has been introduced to give a hexalobular drive recessalternative to the traditional slot used in screws in the BSI range A 204, A 206,A 208 and A 217 to A 221 (a quick reference guide is provided in Anne
13、x A). Thisis intended to alleviate the risks of screw driver blade slippage in the vicinity ofelectronic printed circuit board copper track work and associated wiring.The method of manufacturing choices are more controlled than those of theslotted BS A 204, etc. range, especially for the austenitic
14、corrosion resistant(CRES) steel option, so to better maintain its strength characteristics, e.g. by coldheading and cold rolling threads. This new standards title omits the term“machine” as in “machine screw” to reflect this.This standard also expands the choices by introducing stronger alloy steel,
15、martensitic CRES steel and high temperature/high expansion steel options.The historic thread size of 2-64 UNF has been maintained. However, very fewmating female threaded fasteners such as nuts and helical wire thread inserts,are available commercially; most are 2-56 UNC. Thread size 2-56 UNC hasthe
16、refore been included as a thread size option.This standard does not incorporate a mating range of plain hexagon nuts tomatch the new range of material choices listed above.Any trade name used in this document is information given for the convenienceof users and does not constitute an endorsement.Haz
17、ard warningsCAUTION. Screws conforming to BS A 401 and BS A 411 have cadmium as aplating material, which has been restricted and/or banned in many countriesowing to environmental and health concerns. Users should consult localofficials if they have questions concerning the use of cadmium-plated part
18、s.Use of this documentIt has been assumed in the preparation of this British Standard that theexecution of its provisions will be entrusted to appropriately qualified andexperienced people, for whose use it has been produced.Presentational conventionsThe provisions of this standard are presented in
19、roman (i.e. upright) type. Itsrequirements are expressed in sentences in which the principal auxiliary verb is“shall”.Commentary, explanation and general informative material is presented insmaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publ
20、ication does not purport to include all the necessary provisions of acontract. Users are responsible for its correct application.BRITISH STANDARD BS A 401-420:2015 The British Standards Institution 2015 iiiCompliance with a British Standard cannot confer immunity from legalobligations.BRITISH STANDA
21、RDBS A 401-420:2015iv The British Standards Institution 20151 ScopeThis British Standard specifies the dimensions, materials, protective finishes andpart numbers for 100 countersunk head and pan head screws with unifiedthreads for non-structural general aerospace use.2 Normative referencesThe follow
22、ing documents, in whole or in part, are normatively referenced in thisdocument and are indispensable for its application. For dated references, onlythe edition cited applies. For undated references, the latest edition of thereferenced document (including any amendments) applies.ASD-STAN TR 3775, Aer
23、ospace series Bolts and pins materialsBS 1134, Assessment of surface texture Guidance and general informationBS 1473, Specification for wrought aluminium and aluminium alloys for generalengineering purposes rivet, bolt and screw stockBS 1580-3, Unified screw threads Screw threads with diameters belo
24、w14 in Part 3: RequirementsBS 1872, Specification for electroplated coatings of tinBS 6338, Specification for chromate conversion coatings on electroplated zincand cadmium coatingsBS A 100, Specification for general requirements for bolts and free running nutsof tensile strength not exceeding 1 249
25、MPaBS L 102, Specification for bars and extruded sections ofaluminium-copper-magnesium-silicon-manganese alloy (solution treated andaged at room temperature) (not exceeding 200 mm diameter or minor sectionaldimension) (Cu 4.4, Mg 0.5, Si 0.7, Mn 0.8)BS L 168, Specification for bars and extruded sect
26、ions ofaluminium-copper-magnesium-silicon-manganese alloy (solution treated andartificially aged) (not exceeding 200 mm diameter or minor sectional dimension)(Cu 4.4, Mg 0.5, Si 0.7, Mn 0.8)BS S 80, High chromium-nickel corrosion resisting steel forging stock, bars,forgings and parts (880 to 1 080 M
27、Pa: limiting ruling section 100 mm)BS S 129, Specification for 18/9 chromium-nickel corrosion-resisting steel(titanium stabilized) billets, bars, forgings and parts (540 MPa: limiting rulingsection 150 mm)BS S 130, Specification for 18/9 chromium-nickel corrosion-resisting steel(niobium stabilized)
28、billets, bars, forgings and parts (540 MPa: limiting rulingsection 150 mm)BS S 142, Specification for 1% chromium-molybdenum steel billets, bars, forgingsand parts (9001 100 MPa: limiting ruling section 40 mm)BS S 147, Specification for 0.5% nickel-chromium-molybdenum steel bars for themanufacture o
29、f forged bolts and forged nutsBS S 148, Specification for low nickel-chromium steel (bar for the manufactureof forged bolts only)BS S 154, Specification 212% nickel-chromium-molybdenum steel billets, bars,forgings and parts (8801 080 MPa: limiting ruling section 150 mm)BS S 158, Specification for 1%
30、 chromium-molybdenum steel bars for themanufacture of forged bolts and forged nutsBRITISH STANDARD BS A 401-420:2015 The British Standards Institution 2015 1BS EN 755-2, Aluminium and aluminium alloys Extruded rod/bar, tube andprofiles Mechanical propertiesBS EN 2100, Aluminium alloy AL-P2014A-T4511
31、 Extruded bars and sections a orD 200 mmBS EN 2133, Aerospace series Cadmium plating of steels with specified tensilestrength 1 450 MPa, copper, copper alloys and nickel alloyBS EN 2284, Specification for sulfuric acid anodizing of aluminium and wroughtaluminium alloysBS EN 2398, Aerospace series He
32、at resisting steel FE-PA2601(X6NiCrTiMoV26-15) Rm 900 MPa Bars for machined bolts D 25 mmBS EN 2399, Aerospace series Heat resisting steel FE-PA2601(X4NiCrTiMoV26-15) Rm 900 MPa Bars for forged bolts D 25 mmBS EN 2516, Passivation of corrosion resisting steels and decontamination ofnickel based allo
33、ysBS EN 3911, Aerospace series Six lobe recess Geometrical definitionBS EN 4826, Aerospace series Zinc-nickel (12-16% Ni) plating of steels withspecified tensile strength 1 450 MPa, copper alloys, nickel alloys andaluminium alloys for parts and fastenersBS EN 12163, Copper and copper alloys Rod for
34、general purposesBS EN 12164, Copper and copper alloys Rod for free machining purposesBS EN 12166, Copper and copper alloys Wire for general purposesBS EN ISO 898-1, Mechanical properties of fasteners made of carbon steel andalloy steel Bolts, screws and studs with specified property classes Coarseth
35、read and fine pitch threadSAE AMS 03-19, Electro-deposition of cadmiumSAE AMS 03-25, Sulfuric acid anodizing of aluminium and aluminium alloysSAE AMS 2417, Aerospace material specification, plating, zinc-nickel alloy3 GeneralThe screws shall conform to the relevant requirements of BS A 100 in respec
36、t ofmanufacture, screw threads, identification and marking.NOTE Unless otherwise stated, the measurement and scientific values shown areexpressed in imperial British units with metric SI conversions in parentheses()asneeds be.4 Quality assurance procedureA quality assurance procedure shall be carrie
37、d out in accordance with BS A 100,with the exception of samples for dimensional and non-destructive inspectionwhich shall be taken from each batch in accordance with the levels given inTable 1 of this standard.BRITISH STANDARDBS A 401-420:20152 The British Standards Institution 2015Table 1 Sampling
38、planAcceptable quality level (AQL) Inspection level 11 Inspection level S-11% Thread size Underhead radiusDrive recess dimensions2.5% Burrs and plating (visual) Head concentricityDrive recess form and position4% Nominal lengthOther dimensionsHead height (pan only)Head protrusion (dimension P)(counte
39、rsunk only)5 Material and manufacture5.1 The screws shall be manufactured from the materials listed in Table 2.5.2 The screws shall be manufactured by one of the following methods to suitthe material type and shall meet the final mechanical properties as listed afterany post manufacture heat treatme
40、nt.a) Machined from bright drawn bars. Not applicable to pan head screws madefrom the materials listed in b) below.b) Cold headed from wire or bright drawn bars. This is the minimumrequirement for pan head screws made from aluminium, brass, austeniticCRES steel and low alloy steel.c) Hot forged and
41、machined to suit. Applicable to any suitable material listed.6 Protective finishThe screws shall be coated with the protective treatment for the appropriatematerial as specified in Table 2.7 Freedom from defectsThe screws shall be free from harmful defects, such as thread rolling lapsbetween the nom
42、inal effective diameter and the minor diameter or any cracks.NOTE Screws may be rejected at any time for faults in or revealed by manufacture,even if they have been made from material passed previously for chemicalcomposition and mechanical properties.8 DimensionsWith the exception of the thread, th
43、e screws shall conform to the dimensionsand tolerances given in this standard, prior to applying any protective finish.NOTE 1 Unless otherwise stated, the values given are in inches. For a guide to thethread sizes converted to decimal inch and metric mm, refer to Annex B.NOTE 2 The dimensions and to
44、lerances can be found in Figure 1 to Figure 7inclusive and their associated tables, Table 3 to Table 9 inclusive.NOTE 3 Any dry film lubricant applied as specified in Table 2 might take partsoversize on all features including the thread; this is acceptable.BRITISH STANDARD BS A 401-420:2015 The Brit
45、ish Standards Institution 2015 39 Head of screwsScrew heads shall be concentric with the shank within the dimensional limitsshown in Figure 5 and Figure 6.Drive recesses shall be within the dimensional limits shown in Figure 1 andFigure 2 and shall be positioned central to the heads outside diameter
46、. Therecesses shall be clean and free from burrs upon visual inspection.BRITISH STANDARDBS A 401-420:20154 The British Standards Institution 2015Table2BritishStandardidentifier,materialandfinishofscrews(1 of 3)BritishStandardidentifierTypeofheadMaterialdescription/specificationA)Mechanicalproperties
47、ProtectivefinishD)TensilestrengthC)tons/inch2(MPa)min0.2%proofstresstons/inch2(MPa)minA401100 CountersunkCarbon-manganese(mild)steelinaccordancewithBSENISO898-1,Propertyclass4.625(385)NotstatedinmaterialspecCadmiumcoatedandpassivatedE)inaccordancewithSAEAMS03-19andBS6338,Class2corBSEN2133,coatingCla
48、ss-CA411PanA402100 CountersunkZinc-nickelcoatedandpassivatedinaccordancewithBSEN4826,A3/B3F)orSAEAMS2417Type-2Grade-BInaddition,africtioncontrollubricantG)withaCoefficientofFrictionof0.08to0.14shallbeappliedA412PanA403100 CountersunkAlloysteelinaccordancewithBSS142,BSS147,BSS148,BSS154orBSS158orasli
49、stedinASD-STANTR3775Table-1StrengthClass900B)58(895)45(695)Zinc-nickelcoatedandpassivatedinaccordancewithBSEN4826,A3/B3F)orSAEAMS2417Type-2Grade-BInaddition,africtioncontrollubricantG)withaCoefficientofFrictionof0.08to0.14shallbeappliedA413PanA404100 CountersunkCorrosionresistingsteel(austenitic)inaccordancewithBSS 129orBSS 13035(540)13.5(210)NoneA414PanA405100 CountersunkCorrosionresistingsteel(martensitic)inaccordancewithBSS8057(880)
