ASTM A153

The ASTM A153 standard specifies requirements for zinc coatings (hot-dip galvanizing) applied to iron and steel hardware. It includes several coating classes based on the type of product and its intended use.

In 2005, ASTM introduced a newer specification, ASTM F2329, specifically developed for hot-dip galvanizing of fasteners such as bolts, screws, nuts, and washers. This standard was designed to replace ASTM A153 Class C and provides requirements better suited for threaded fasteners. Although F2329 is increasingly being adopted across industries, many older technical manuals and references still list A153 due to less frequent updates.

Additionally, ASTM A123 is another related galvanizing specification that applies to structural steel products such as plates, bars, strips, rolled shapes, pressed shapes, and castings. The equivalent standard issued by AASHTO (American Association of State Highway and Transportation Officials) for ASTM A153 is AASHTO M232.

Zinc Coating Thickness Requirements by Class :

Class	Application / Description	Avg. Coating Thickness (mils)	Min. Coating Thickness (mils)
Class A	Steel, malleable iron parts, and castings	3.4	3.1
Class B	Rolled, forged, or pressed items not listed under Class C or D	See B-1 to B-3	See B-1 to B-3
Class B-1	Sections = 3/16" thick and longer than 15"	3.4	3.1
Class B-2	Sections < 3/16" thick and longer than 15"	2.6	2.1
Class B-3	Any thickness, with length = 15"	2.2	1.9
Class C	Bolts over 3/8" dia. and similar parts; washers 3/16"–1/4" thick	2.1	1.7
Class D	Bolts 3/8" dia. & below, rivets, nails, and washers < 3/16" thick	1.7	1.4