Global Fastener News

By Frederick Graves, P.E.

F.E. Graves Associates
December 27, 1979 FIN – Over the past 18 months there have been several important revisions to the ASTM Specifications covering a these products. The following information will bring you up to date on current specifications.
Also included are the “basis of purchase” clauses for A325 and A490 structural bolts, and suitable nuts.

Heavy Head Short Thread Length High Strength Structural Bolts
There are three types of A325 structural bolts:
Type 1 – Bolts made from medium carbon steel, quenched and tempered.
Type 2 – Bolts made from low-carbon martensitic steel, quenched and tempered.
Type 3 – Bolts made from steels having atmospheric corrosion resistance and weathering characteristics, quenched and tempered.

Either Type 1 or Type 2 bolts may be supplied unless other specified. Type 3 may be supplied when agreed to by purchaser.

There are two types of A490 structural bolts:
Type 1 – Bolts made from medium-carbon alloy steel, quenched and tempered.
Type 2 – Bolts made from medium-carbon alloy steels having atmospheric corrosion resistance and weathering characteristics, quenched and tempered.

When no bolt type is specified, Type 1 bolts shall be supplied. Type 3 bolts may be supplied when agreed upon by purchaser.

Heavy Hex Structural Nuts
Originally included in the structural bolt specifications i.e. A325 and A490 the specifications for heavy hex structural nuts are now covered in ASTM A563.
Listed below is a tabulation of A563 heavy hex structural and designations as related to the appropriate structural bolt designation.
A563 Nut Designation Grade                Applicable Structural Bolt Type
C                                                A325 (Types 1 & 2)
C3                                                A325 (Type 3)
DH (1) (2) (3)                                    A490 (Type 1)
DH3                                            A490 (Type 3)

Notes: (1) Heat treated heavy hex nuts meeting the requirements for ASTM A194 Grade 2 H may be furnished at the option of the supplier.
(2) Galvanized heavy hex nuts for use with galvanized bolts shall be Grade DH or Grade 2H tapped oversize in accordance with A563.
(3) Either Grade DH or Grade 2H heavy hex nuts may be substituted for Grade C nuts.

Metric Structural Bolt & Nut Designations
Basically the metric structural bolt designations consist only of adding the letter “M” to the inch-series designations, ie.e A325 M, Type 1; A490 M, Type 1; etc.
Metric structural nut designations vs. inch-series structural nuts are as follows:
Inch                                        Metric
C                                            8S
C3                                            8S 3
DH                                            10S
DH3                                        10S 3

Structural Washers
All structural washers – circular, beveled and clipped – are through hardened (quenched and tempered) and are now covered in the ASTM A436 specification. All washers shall be marked with the manufacturer’s identification symbol, plus the numeral “3” if made from weathering steel, and the letter “M” if metric.
Upcoming issues of FIN’s Technical Viewpoint will include further information on new developments in fastener specifications – including corrosion resistant coatings, more metrics, flanged products, etc. ©1979/2013 Fastener Industry News.
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