Your search did not yield any results

Site Pages

Dr. Galv KnowledgeBase


ASTM A153 governs zinc coatings applied by the hot-dip process to hardware products such as castings, fasteners, rolled, pressed, and forged products, and miscellaneous threaded objects that will be centrifuged, spun, or otherwise handled to remove excess zinc. The hot-dip galvanizing process for articles galvanized to ASTM A153 is identical to the process required under ASTM A123 with the exception the iron and steel hardware in ASTM A153 are centrifuged or spun to remove excess zinc.

Get the Latest HDG Specifications

ASTM A153/A153M Requirements

  • Coating Thickness/Weight depends on the material category and steel thickness, values are listed in Table 3
  • Threaded Products areas with threads are not subject to the coating thickness requirement
  • Finish continuous, smooth, uniform
  • Embrittlement high tensile strength fasteners (>150ksi) and castings can be subject to embrittlement
  • Appearance free from uncoated areas, blisters, flux deposits and gross dross inclusions as well as having no heavy zinc deposits that interfere with intended use
  • Adherence the entire coating should have a strong adherence throughout the service life of hot-dip galvanized steel

There are fabrication steps that may impair the corrosion protection of the hot-dip galvanized coating; however, flaking or damage to the coating because of this is not case for rejection. In all cases, good steel selection results in the formation of a higher quality coating and finish on the product. The corrosion protection coating for threaded products is applied after the product has been fabricated and further fabrication may compromise the corrosion protection system. The one exception to this rule is the internal threads of a nut that should be over-tapped after the coating is applied in order to accommodate the coating thickness change on the thread of the bolts. In this case, the zinc on the bolt threads provides the corrosion protection to the uncoated threads in the nut.

There are certain fabrication techniques that can induce stresses into the steel and lead to brittle failure. There are precautions given in ASTM A143/A143M that should be taken in order to prevent embrittlement. In addition, selecting steels with appropriate chemistries can help prevent embrittlement of malleable castings. A reproduction and summary of the table given in ASTM A153/A153M, (Table 3), gives the different classes of products and the minimum coating thickness required by the specification.

Table 3

Thickness or Weight (Mass) of Zinc Coating for Various Classes of Material
Weight (Mass) of Zinc Coating,
oz/ft2 (g/m2) of Surface, minimum
Coating Thickness, mils
(microns), Minimum
Class of MaterialAverage of Specimens TestedAny Individual Specimenverage of Specimens TestedAny Individual Specimen
Class A - Castings - Malleable Iron, Steel2.00 (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)

B-1: > 5/8” (15.88 mm) and > 15” (381 mm) in length

2.00 (610)1.80 (550)3.5 (85)3.1 (79)

B-2: < 5/8” (15.88 mm) and > 15” (381 mm) in length

1.5 (458)1.25 (381)2.6 (66)2.1 (53)
B-3: any thickness and < 15” (381 mm) in length1.30 (397)1.10 (336)2.2 (56)1.9 (48)
Class C - Fasteners > 3/8” (9.52 mm) in diameter. Washers > 3/16” (4.76 mm) in thickness.1.25 (381)1.00 (305)2.1 (53)1.7 (43)
Class D - Fasteners < 3/8” (9.52 mm) in diameter. Rivets, nails and similar articles. Washers < 3/16” (4.76 mm) in thickness.1.00 (305)0.85 (259)1.7 (43)1.4 (36)
Note 1: Length of the piece, stated in Classes B-1, B-2, B-3, refers to the finished dimensions of the piece after fabrication

Related Articles:

A123 vs. A153 for Hardware Assemblies

ASTM F2329 vs. ASTM A153

Galvanized Embed Parts Meeting ASTM A153 Requirements

Fastener Quality Act and ASTM A153

Hot-Dip Galvanized Fasteners

Was this answer helpful? YES       | NO

Are you still looking for the right answer? Ask an Expert