IS 3757


1. Scope and Field of Application : Covers the requirements for large series hexagon, high strength structural steel bolts in property classes 8.8 and 10.9 and in the size range M 16 to M36 with short thread lengths suitable for use in both friction-type and bearing-type structural steel joints. Bolts to this standard when matched with the appropriate nuts have been designed to provide an assembly with a high level of assurance against failure by thread stripping on over tightening.
2. Dimensions and Tolerances :
Attention is drawn to the importance of ensuring that the bolts are correctly used if satisfactory results are to be obtained.
2.1 The dimensions of the bolts shall be as given in Table 1.
2.2 The recommended length-size combinations shall be as given in Table 2.
2.3 Threads shall conform to tolerance class 6g of IS : 4218 (Part 6)-1978 ‘ISO metric screw threads: Part 6 Limits of sizes for commercial bolts and nuts (diameter range 1 to 52 mm) ( first revision )’. In case of hot-dip galvanized bolts, the specified tolerance class shall apply before hot-dip galvanizing.
3. Grade : Unless otherwise specified, the bolts shall be of product grade C as specified in IS : 1367 (Part 2)-1979 ‘Technical supply conditions for threaded steel fasteners: Part 2 Product grades and tolerances ( second revision )’.
4. Mechanical Properties :
The bolts shall be of property class 8.8 or 10.9 as specified in IS : 1367 (Part 3)-1979 ‘Technical supply conditions for threaded steel fasteners: Part 3 Mechanical properties and test methods for bolts, screws and studs with full load ability ( second revision )’.
4.1 For tensile, proof load and wedge loading test on full size bolts only four threads shall be exposed between the grips. This is obtained by freely running the nut or fixture to the fullest extent and then unscrewing the specimen four full turns.
4.2 For test purposes, the screw threads on hot-dip galvanized bolts shall be chemically stripped to permit assembly with a standard threaded grip or nut, that is, thread class 6H.
5. Finish :
5.1 Unless specified otherwise, the bolts shall be supplied in the dull black heat-treated condition with a residual coating of light oil.
5.2 Where property class 8.8 bolts are required to be hot-dip galvanized, they shall be galvanized in accordance with the requirements of IS : 1367 (Part 13)-1983 ‘Technical supply conditions for threaded steel fasteners: Part 13 Hot-dip galvanized coatings on threaded fasteners ( second revision )’. For fasteners with hot-dip galvanized coatings, the bolts or the mating nuts shall be provided with a suitable lubricant which shall be clean and dry to the touch to ensure that seizure shall not take place in assembly. The hot-dip galvanized bolts shall be subjected to the anti-seizing test as specified in Appendix A.
Note : Bolts of property class 10.9 should not be hot-dip galvanized since this may cause hydrogen embrittlement.
6. General Requirements :
6.1 In regard to permissible surface discontinuities, the bolts shall conform to IS : 1367 (Part 9)-1979 ‘Technical supply conditions for threaded steel fasteners: Part 9 Surface discontinuities on bolts, screws and studs ( second revision )’.
6.2 In regard to requirements not covered in the standard, the bolts shall conform to IS : 1367 (Part 1)-1980 ‘Technical supply conditions for threaded steel fasteners: Part 1 Introduction and general information ( second revision )’.
6.3 The high strength structural nuts to be used with these bolts shall conform to the requirements of IS : 6623-1985 ‘High strength structural nuts ( first revision )’.
6.3.1 These nuts shall be of the property class and finish for each type of bolt as follows:

Bolt Property Class and Finish
8.8S, dull black
8.8S, hot-dip galvanized
10.9S, dull black
Nut Property Class and Finish
8S or 10S, dull black
10S, hot-dip galvanized
10S, dull black
6.4 Hardened and tempered washers to be used with these bolts shall conform to the requirements of IS : 6649-1985 ‘Hardened and tempered washers for high strength structural bolts and nuts ( first revision )’.
7. High strength structural bolts shall be designated by name, size, nominal length, the number of this standard and the property class identification symbol 8.8S or 10.9S—the suffix letter S denotes a high strength structural bolt with a large series hexagon head. In case of hot dip galvanized bolts, the word ‘galvanized’ shall be added to the designation. Example:
A high strength structural bolt of size M24, length 140 mm, property class 8.8 and galvanized shall be designated as:
High Strength Structural Bolt M24 × 140 IS : 3757—8.8S galvanized
7.1 If the bolt in the above example is required with a hot-dip galvanized high strength structural nut ( see IS : 6623-1985 ), the letter N shall be added to the designation as follows:
High Strength Structural Bolt M24 × 140 N IS : 3757—8.8S galvanized
8. Sampling : Sampling and criteria of acceptance shall be in accordance with IS : 2614-1969 ‘Methods for sampling of fasteners ( first revision )’.


High strength structural bolts shall be marked with the following symbols on the top surface of the bolt head, either embossed or indented, as shown below :

  • The KE identification symbol, and
  • The property class identification symbol 8S for 8.8S or 10S for 10.9S. Minimum height of markings shall be 4.0 mm. When embossed, markings shall project not less than 0.3 mm above the surface of the head and total head height (head plus markings) shall not exceed the specified maximum head height plus 0.4 mm.


A-1. Where bolts and the mating nuts and washers with hot-dip galvanized coating are specified, these shall be subject to the following anti-seizing test for testing the effectiveness of the lubricant coating applied to the hot-dip galvanized bolts or nuts:
a) The test shall be carried out on bolts, nuts and washers in the condition as supplied by the KE and shall be in accordance with, and include a lubricant coating as required by
5.2. There shall be no other lubricant applied for the purpose of this test. If the test is performed by the user it shall be carried out immediately after receipt of the bolts, nuts and washers from the KE.
b) The bolt with nut and washer selected for testing shall be placed with the washer directly under the nut in a steel joint with total thickness so that three to five full threads of the bolt are located between the bearing surfaces of the bolt head and nut. The diameter of the holes in the assembly shall have the same nominal diameter as the hole in the washer.
c) The nut shall be initially tightened to produce a load in the bolt not less than 10 present of the specified proof load. After this initial tightening, the bolt and the nut position shall be marked to provide the starting point for the rotational movement to be measured. During nut rotation the bolt head shall be restrained from turning, and the final tensioning shall be completed without stopping the motion of the nut. The nut shall be rotated in accordance with the requirements of Table 3 from the initial tightening position without fracture of the bolt, or stripping of the bolt or nut thread.