1、BRITISH STANDARD BS 3409-2: 1966 Incorporating Amendment Nos. 1 and 2 Specification for The tapping of holes to receive wire thread inserts (UNC and UNF threads) Part 2: Diameters below 1 / 4inBS3409-2:1966 This British Standard, having been approved by the MechanicalEngineering IndustryStandards Co
2、mmittee and endorsed by the Chairman ofthe Engineering Divisional Council, was published under theauthority of the General Councilon 31 January1966 BSI 03-2000 The following BSI references relate to the work on this standard: Committee reference MEE/148 Draft for comment D65/1299 ISBN 0 580 35793 7
3、Co-operating organizations The Mechanical Engineering Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: The Government departments and scientific
4、 and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the Committee entrusted with the preparation of this standard: Associated Offices Technical Committee Institution of Heating and Ventilating Association of Consulting En
5、gineers Engineers Association of Mining Electrical and Institution of Mechanical Engineers Mechanical Engineers Institution of Mechanical Engineers Board of Trade (Automobile Division) British Chemical Plant Manufacturers Institution of Production Engineers Association Locomotive and Allied Manufact
6、urers British Compressed Air Society Association of Great Britain British Electrical and Allied Manufacturers London Transport Board Association* Machine Tool Trades Association British Gear Manufacturers Association Ministry of Defence, Army Department* British Internal Combustion Engine Ministry o
7、f Defence, Navy Department* Manufacturers Association Ministry of Labour (H.M. Factory British Iron and Steel Federation Inspectorate) British Mechanical Engineering Federation Ministry of Power British Railways Board Ministry of Public Building and Works Crown Agents for Oversea Governments and Min
8、istry of Technology National Administrations Engineering Laboratory Electricity Council, the Generating Board Ministry of Transport and the Area Boards in England and Wales National Coal Board Engineering Equipment Users Association National Physical Laboratory (Ministry of Gas Council Technology) I
9、nstitute of Marine Engineers Radio Industry Council Institution of Civil Engineers Royal Institute of British Architects Institution of Gas Engineers British Plastics Federation Society of British Aerospace Companies Gauge and Tool Makers Association Limited Institute of the Motor Industry (Incorpor
10、ated) Society of Motor Manufacturers and Traders Ministry of Aviation Limited Screw Thread Tool Manufacturers Individual manufacturers Association Amendments issued since publication Amd. No. Date of issue Comments 5999 January 1967 1181 May 1973 Indicated by a sideline in the marginBS3409-2:1966 BS
11、I 03-2000 i Contents Page Co-operating organizations Inside front cover Foreword ii Section 1. Tapped holes 1 Scope 1 2 Form of thread and limits of size 1 3 Identification 1 Section 2. Screwing taps 4 General dimensions 4 5 Marking 4 6 Form of thread 4 7 Limits of sizes for cutting diameter 4 Secti
12、on 3. Gauging system 8 General 8 9 Design and general dimensions 8 10 Tolerances and limits of size 8 Figure 1 Basic form of Unified insert assembly 2 Table 1 Limits and tolerances suitable for tapped holes for inserts for UNC threads, Class 2B 1 Table 2 Limits and tolerances suitable for tapped hol
13、es for inserts for UNF threads, Class 2B 3 Table 3 General dimensions of UNC taps for insert tapped holes 4 Table 4 General dimensions of UNF taps for insert tapped holes 5 Table 5 Tolerances on general dimensions of taps for insert tapped holes 6 Table 6 Limits of size for UNC taps for insert tappe
14、d holes 7 Table 7 Limits of size for UNF taps for insert tapped holes 7 Table 8 Tolerances for GO gauges for UNC insert tapped holes 8 Table 9 Tolerances for GO gauges for UNF insert tapped holes 8 Table 10 Tolerances for NOT GO gauges for UNC insert tapped holes 8 Table 11 Tolerances for NOT GO gau
15、ges for UNF insert tapped holes 8 Table 12 Tolerances for GO and NOT GO plain plug gauges for minor diameters 9 Table 13 Limits of size for GO gauges for UNC insert tapped holes 9 Table 14 Limits of size for NOT GO gauges for UNC insert tapped holes 9 Table 15 Limits of size for GO gauges for UNF in
16、sert tapped holes 9 Table 16 Limits of size for NOT GO gauges for UNF insert tapped holes 9BS3409-2:1966 ii BSI 03-2000 Foreword This standard makes reference to the following British Standards: BS 919, Screw gauge limits and tolerances Part 1: Gauges for screw threads of Unified form. BS 949, Screw
17、ing taps Part 2: Taps for Unified threads. BS 1044, Gauge blanks Part 1: Plug, ring and calliper gauges. BS 1580, Unified screw threads Part 3: Diameters below 1 / 4in. When BS3409 was issued in1961 it made provision for Unified tapped holes in sizes 1 / 4 in and over as recognition of Unified threa
18、ds below 1 / 4in was restricted to five selected sizes. Since that time, not only has the use of what are commonly known as the “numbered sizes” increased considerably, but the complete series with UNC and UNF threads has been incorporated in ISO Recommendation263 where it forms part of the internat
19、ional system of screw threads in inch units and is now covered by a British Standard, namely,BS1580, Part 3. It therefore seemed desirable to extend the range of BS3409 to provide tapped holes for wire thread inserts in these sizes and Part2 has accordingly been prepared. As in the earlier standard,
20、 now known as Part 1, this part does not standardize the inserts themselves, but specifies limits of sizes for tapped holes which, when assembled with an insert, will give the required nominal size and class of tolerance of the internal thread in question. Unlike Part 1, this standard provides only
21、for Class2B holes as there are no Class1B tolerances for Unified threads in sizes below 1 / 4in. It should also be noted that, in the case of the minor diameter, the committee responsible for this specification have felt obliged to depart from the principle of adhering strictly to the Unified tolera
22、nce formulae. This has been necessary because the formula in question contains a constant which results in a large tolerance and consequent risk of too great a reduction in the possible depth of engagement on the smaller sizes. Tolerances which are two thirds of the values obtained by the standard f
23、ormula have therefore been adopted for this element; it should be noted that they are based on the minimum major diameter of the hole for the insert and not on the nominal major diameter of the thread in question. A British Standard does not purport to include all the necessary provisions of a contr
24、act. 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 and ii, pages1to 9 and a back cover. Thi
25、s 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.BS3409-2:1966 BSI 03-2000 1 Section 1. Tapped holes 1 Scope This British Standard comprises three sections: Section 1, which specifies li
26、mits of size for tapped holes to accommodate wire thread inserts to provide thread sizes from No. 2 to No. 12UNC and UNF; Section 2, which recommends screwing taps intended to produce holes to the limits of size specified in Section 1; Section 3, which gives a recommended gauging system for checking
27、 the tapped holes. 2 Form of thread and limits of size Holes shall be threaded to provide Class2B limits in accordance with BS1580, Part 3 1)when fitted with the wire thread inserts and shall be of ISO/Unified form as illustrated in Figure 1. Holes for inserts for UNC threads shall be tapped to the
28、limits specified in Table 1 and those for inserts for UNF threads shall be tapped to the limits specified inTable 2. NOTEThe limits given in Table 1 and Table 2 are designed to permit the production, under normal conditions, of holes to suit the class of thread stated. Under ideal conditions it may
29、be possible to achieve a closer class of fit on the final installation than that indicated in the table. 3 Identification In order to distinguish requirements for holes intended to receive inserts from those intended to receive threaded components it is recommended that the former be clearly identif
30、ied on drawings and specifications. This may be done by specifying the actual major, effective and minor diameters of the holes and their limits or by the addition of the words “wire insert” and number of this British Standard to the designation of the thread, e.g.6-32UNC-2B,Wire inset, BS3409, Part
31、 2. Table 1 Limits and tolerances suitable for tapped holes for inserts for UNC threads, Class 2B a 1) BS1580, “Unified screw threads”, Part 3, “Diameters below 1 / 4in”. 1 2 3 4 5 6 7 8 Designation Major diameter Effective diameter Minor diameter Min. Max. Tol. Min. Max. Tol. Min. in in in in in in
32、 in 2-56 UNC 3-48 UNC 4-40 UNC 0.109 2 0.126 1 0.144 5 0.098 9 0.113 9 0.129 8 0.001 3 0.001 4 0.001 6 0.097 6 0.112 5 0.128 2 0.094 1 0.108 0 0.122 4 0.004 2 0.004 5 0.005 0 0.089 9 0.103 5 0.117 4 5-40 UNC 6-32 UNC 8-32 UNC 0.157 5 0.178 6 0.204 6 0.142 9 0.160 1 0.186 2 0.001 7 0.001 8 0.001 9 0.
33、141 2 0.158 3 0.184 3 0.135 1 0.150 3 0.175 8 0.004 7 0.005 5 0.005 0 0.130 4 0.144 8 0.170 8 10-24 UNC 12-24 UNC 0.244 1 0.270 1 0.219 3 0.245 4 0.002 2 0.002 3 0.217 1 0.243 1 0.205 1 0.230 8 0.006 1 0.005 8 0.199 0 0.225 0 a See note to Clause 2.BS 3409-2:1966 2 BSI 03-2000 Figure 1 Basic form of
34、 Unified insert assemblyBS3409-2:1966 BSI 03-2000 3 Table 2 Limits and tolerances suitable for tapped holes for inserts for UNF threads, Class 2B a 1 2 3 4 5 6 7 8 Designation Major diameter Effective diameter Minor diameter Min. Max. Tol. Min. Max. Tol. Min. in in in in in in in 2-64 UNF 3-56 UNF 4
35、-48 UNF 0.106 3 0.122 2 0.139 1 0.097 4 0.111 9 0.127 0 0.001 2 0.001 3 0.001 5 0.096 2 0.110 6 0.125 5 0.093 1 0.106 8 0.120 7 0.003 7 0.003 9 0.004 2 0.089 4 0.102 9 0.116 5 5-44 UNF 6-40 UNF 8-36 UNF 0.154 5 0.170 5 0.200 1 0.141 4 0.155 9 0.183 9 0.001 6 0.001 7 0.001 9 0.139 8 0.154 2 0.182 0 0
36、.134 2 0.147 8 0.174 5 0.004 3 0.004 4 0.004 5 0.129 9 0.143 4 0.170 0 10-32 UNF 12-28 UNF 0.230 6 0.262 4 0.212 3 0.241 3 0.002 0 0.002 1 0.210 3 0.239 2 0.201 5 0.228 7 0.004 7 0.005 0 0.196 8 0.223 7 a See note to Clause 2.BS3409-2:1966 4 BSI 03-2000 Section 2. Screwing taps 4 General dimensions
37、Recommended dimensions of screwing taps for UNC holes are in accordance withTable 3 and those of screwing taps for UNF holes are in accordance withTable 4. The tolerances on general dimensions are in accordance withTable 5. 5 Marking Taps for holes intended to receive inserts shall be marked with th
38、e designation appropriate to the thread and, in addition, with the words “Wire insert” and the number of this British Standard, e.g. 4-40 UNC 2B Wire insert BS 3409 6 Form of thread The form of thread of the screwing taps shall be in accordance with BS949 for ISO inch threads. 7 Limits of sizes for
39、cutting diameter The limits of size for the cutting diameter of UNC taps are as given in Table 6 and those for UNF taps are as given inTable 7. NOTEThe tolerances are calculated in accordance with the formula specified for ZONE2 taps in BS949 2) , the formula being applied to the actual major diamet
40、er of the tapped hole and not to the nominal size by which it is known. Table 3 General dimensions of UNC taps for insert tapped holes 2) BS949, “Screwing taps”. 1 2 3 4 5 6 7 8 9 10 11 Diameter No. of threads per inch No. of flutes Overall length Length of thread Diameter of shank Square Recess Nom
41、inal Minimum major Size Length Diameter Length L l d 1 a l 2 d 2 l 1 in mm Left to manufacturers discretion mm mm mm mm mm mm mm No. 2(0.026) No. 3(0.099) No. 4(0.112) 2.812 3.249 3.716 56 48 40 48 50 53 11 13 13 3.15 3.55 4.00 2.50 2.80 3.15 5 5 6 2.12 2.50 2.80 7 7 8 No. 5(0.125) No. 6(0.138) No.
42、8(0.164) 4.046 4.590 5.250 40 32 32 53 58 62 13 16 17 4.50 5.00 5.60 3.55 4.00 4.50 6 7 7 3.15 3.55 4.25 8 9 9 No. 10 (0.190) No. 12 (0.216) 6.261 6.922 24 24 66 66 19 19 6.30 7.10 5.00 5.60 8 8 4.50 5.30 11 11BS3409-2:1966 BSI 03-2000 5 Table 4 General dimensions of UNF taps for insert tapped holes
43、 1 2 3 4 5 6 7 8 9 10 11 Diameter No. of threads per inch No. of flutes Overall length Length of thread Diameter of shank Square Recess Nominal Minimum major Size Length Diameter Length L l d 1 a l 2 d 2 l 1 in mm Left to manufacturers discretion mm mm mm mm mm mm mm No. 2(0.086) No. 3(0.099) No. 4(
44、0.112) 2.738 3.142 3.579 64 56 48 44.5 48 50 9.5 11 13 2.80 3.15 3.55 2.24 2.50 2.80 5 5 5 2.12 2.50 6 7 7 No. 5(0.125) No. 6(0.138) No. 8(0.164) 3.973 4.376 5.136 44 40 36 53 53 62 13 13 17 4.00 4.50 5.60 3.15 3.55 4.50 6 6 7 2.80 3.15 4.25 8 8 9 No. 10 (0.190) No. 12 (0.216) 5.911 6.718 32 28 66 6
45、6 19 19 6.30 7.10 5.00 5.60 8 8 4.50 5.30 11 11BS3409-2:1966 6 BSI 03-2000 Table 5 Tolerances on general dimensions of taps for insert tapped holes a. Tolerances on shanks and squares Dimensions in millimeters 1 2 3 4 5 6 7 Shank diameter d 1Square size a Tolerance on shank diameter d 1 Square Toler
46、ance A / F a Tolerance on length of square Ground thread taps Shank Non-ground thread taps Shank Ground taps Non-ground taps Over Including (h9) (h11) (h11) (h12) l 2 0 3 +0 0.025 +0 0.060 +0 0.060 +0 0.100 0.8 3 6 +0 0.030 +0 0.075 +0 0.075 +0 0.120 6 10 +0 0.036 +0 0.090 +0 0.090 +0 0.150 10 18 +0
47、 0.043 +0 0.110 +0 0.110 +0 0.180 18 30 +0 0.052 +0 0.130 +0 0.130 +0 0.210 1.6 30 50 +0 0.062 +0 0.160 +0 0.160 +0 0.250 50 56 +0 0.074 +0 0.190 +0 0.190 +0 0.300 b. Tolerances on overall length and length of thread Dimensions in millimeters 1 2 3 Nominal diameter of tap Tolerance on overall length
48、 and length of thread Over Including L and l 0 5.5 +0 2.5 5.5 12.0 +0 3.2 12.0 39.0 +0 5.0 39.0 101.6 +0 6.3BS3409-2:1966 BSI 03-2000 7 Table 6 Limits of size for UNC taps for insert tapped holes Table 7 Limits of size for UNF taps for insert tapped holes 1 2 3 4 5 6 7 Designation Major diameter Eff
49、ective diameter Tolerance on included angle Min. Basic Max. Tol. Min. in in in in in deg. 2-56 UNC 3-48 UNC 4-40 UNC 0.110 7 0.127 9 0.146 3 0.097 6 0.112 5 0.128 2 0.098 3 0.113 4 0.129 1 0.000 2 0.000 3 0.000 3 0.098 1 0.113 1 0.128 8 1.9 1.7 1.6 5-40 UNC 6-32 UNC 8-32 UNC 0.159 3 0.180 7 0.206 7 0.141 2 0.158 3 0.184 3 0.142 1 0.159 3 0.185 3 0.000 3 0.000 3 0.000 3 0.141 8 0.159 0 0.185 0 1.6 1.4 1.4 10-24 UNC 12-24 UNC 0.246 5 0.272 5 0.217 1 0.243 1 0.218 2
