This document provides specifications for high strength structural bolts used in structural steel joints. It specifies requirements for bolts in sizes M16 to M36 made of steel with property classes 8.8 and 10.9. The document defines dimensions, tolerances, mechanical properties, finishes, testing and marking requirements. It specifies that bolts must be matched with nuts and washers conforming to other Indian Standards to provide assemblies with high strength and resistance to failure from overtightening. Hot-dip galvanized bolts are also covered, with additional specifications for lubrication and anti-seize testing to prevent galling during assembly.
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Indian standard specification for high strength structural bolts
4. IS : 3757 - 1985
4
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:
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. Designation — 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 )’.
9. Marking — 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:
a) The manufacturer’s identification symbol, and
b) 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.
10. Mode of Delivery — The bolts shall be delivered in accordance with IS : 1367 (Part 18)-1979
‘Technical supply conditions for threaded steel fasteners: Part 18 Marking and mode of delivery
( second revision )’.
11. Certification Marking — Details available with the Bureau of Indian Standards.
Bolt Property Class and Finish Nut Property Class and Finish
8.8S, dull black 8S or 10S, dull black
8.8S, hot-dip galvanized 10S, hot-dip galvanized
10.9S, dull black 10S, dull black
5. IS : 3757 - 1985
5
A P P E N D I X A
( Clause 5.2 )
ANTI-SEIZING TEST FOR HOT-DIP GALVANIZED FASTENERS
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:
E X P L A N A T O R Y N O T E
IS : 3757 ‘Specification for high tensile friction grip fasteners for structural engineering
purposes was originally published in 1966. The first revision of IS : 3757 catered for high tensile
friction grip bolts only; the corresponding nuts and washers were covered by separate standards.
In the present revision of IS : 3757, the title of the standard has been changed to ‘High strength
structural bolts’ to enable them to be used for both friction-type and bearing type of structural
steel connections with the same bolting installation procedure. Further, shorter thread lengths
have been provided to ensure no thread protrusion in the shear plane so that higher working
stresses can be adopted for bearing-type connections. Also due to technical reasons, the width
across flats for M20 size has been changed from 32 to 34 mm in line with IS : 9519-1980 ‘Width
across flats for hexagon head bolts and nuts’. It is, however, recognized that some transition period
would be essential during which the new across flat size would be introduced and the old across
a) The test shall be carried out on bolts, nuts and washers in the condition as supplied by the
manufacturer 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 manufacturer.
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 percent 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.
TABLE 3 NUT ROTATION REQUIREMENTS
Bolt Length (Nominal) Nut Rotation ( Min )
/ 2d 180º
2d < / 3d 240º
3d < / 4d 300º
4d < / 8d 360º
/ > 8d 420º
6. IS : 3757 - 1985
6
flat size phased out. During this transition period, the bolts may be supplied with the old across
flat size and other related dimensions as mentioned below as being functionally equivalent.
However, bolts with old across flat site should not be supplied with nuts with new across flat size
and vice-versa.
The standard is based on ISO/DIS 7412 ‘High strength structural bolts (short thread length
type)’ issued by the International Organization for Standardization.
This edition 3.2 incorporates Amendment No. 1 (October 1987) and Amendment No. 2
(July 1989). Side bar indicates modification of the text as the result of incorporation of the
amendments.
All dimensions in millimetres.
Thread Size d M20
s
Max 32
Min 31
e Min 35.03
dw
Max s actual
Min 29.5