ASTM A153 – Specification

ASTM A153/A153M specification governs the standards for hot-dip zinc coatings applied specifically to iron and steel hardware. This process involves immersing parts in molten zinc to create a metallurgical reaction, resulting in alloy layers that bond the coating to the steel surface.This standard is primarily designed for hardware items that are centrifuged or mechanically handled to remove excess zinc, making it a critical reference for fasteners, castings, and rolled or forged articles. It establishes rigorous requirements for minimum coating weight and thickness based on the material category and size. Beyond thickness, the specification also outlines essential quality benchmarks for adherence, finish, and protection against embrittlement.

Coating Properties

The following table details the minimum coating requirements mandated by ASTM A153. These values ensure the durability and corrosion resistance of hardware used in demanding structural and industrial applications.

Thickness or Weight [Mass] of Zinc Coating
Class of Material Weight [Mass] of Zinc Coating, oz/ft² [g/m²] of Surface, Minimum Coating Thickness, mils [microns], Minimum
Average of Specimens Tested Any Individual Specimen Average of Specimens Tested Any Individual Specimen
Class A—Castings—Malleable Iron, Steel 2.00 [610] 1.80 [550] 3.4 [86] 3.1 [79]
Class B—Rolled, pressed, and forged articles (except those which would be included under Classes C and D): See B-1 through B-3 See B-1 through B-3 See B-1 through B-3 See B-1 through B-3
B-1—3/16 in. [4.76 mm] and over in thickness and over 15 in. [381 mm] in length 2.00 [610] 1.80 [550] 3.4 [86] 3.1 [79]
B-2—under 3/16 in. [4.76 mm] in thickness and over 15 in. [381 mm] in length 1.50 [458] 1.25 [381] 2.6 [66] 2.1 [53]
B-3—any thickness and 15 in. [381 mm] and under in length 1.30 [397] 1.10 [336] 2.2 [56] 1.9 [48]
Class C—Fasteners over 3/8 in. [9.52 mm] in diameter and similar articles. Washers 3/16 in. and 1/4 in. [4.76 and 6.35 mm] in thickness 1.25 [381] 1.00 [305] 2.1 [53] 1.7 [43]
Class D—Fasteners 3/8 in. [9.52 mm] and under in diameter, rivets, nails and similar articles. Washers under 3/16 in. [4.76 mm] in thickness 1.00 [305] 0.85 [259] 1.7 [43] 1.4 [36]
Note: Length of the piece, stated in Classes B-1, B-2, and B-3, refers to the finished dimension of the piece after fabrication.