ASTM A123
Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products
Specifies batch hot-dip galvanized zinc coatings on fabricated and unfabricated iron and steel products.
What ASTM A123 specifies
ASTM A123/A123M is the standard for batch hot-dip galvanizing of structural shapes, plate, bar, strip, pipe, tubing, wire work, forgings, and castings. Required average coating grade depends on both measured steel thickness and material category, ranging from Grade 35 for thin wire to Grade 100 for heavy structural, reinforcing, forged, or cast work. The grade number equals micrometres of average zinc thickness; individual specimens may be one listed grade lower. Fabrication should include drainage and venting before galvanizing. Buyers should identify significant appearance constraints, repair limits, masking, threads, and any special sampling.
ASTM A123 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Thickness | Coating weight | Requirement / test |
|---|---|---|---|---|
Structural shapes | Grades 45, 65, 75, 75, 100, and 100 across steel-thickness bands from <1.6 to ≥16 mm. | 45–100 µm 1.8–3.9 mil | Grade number equals average thickness in µm. | Magnetic thickness or stripping mass. |
Plate, strip, and bar | Grades 45, 65, 75, 75, 75, and 100 across the six thickness bands. | 45–100 µm 1.8–3.9 mil | Grade number equals average thickness in µm. | Magnetic thickness or stripping mass. |
Pipe and tubing | Grades 45, 45, 75, 75, 75, and 75 across the six thickness bands. | 45–75 µm 1.8–3 mil | Grade number equals average thickness in µm. | Magnetic thickness or stripping mass. |
Wire | Grades 35, 50, 60, 65, 80, and 80 across the six thickness bands. | 35–80 µm 1.4–3.1 mil | Grade number equals average thickness in µm. | Magnetic thickness or stripping mass. |
Forgings and castings | Grade 100 for applicable products at least 4.8 mm thick. | ≥ 100 µm ≥ 3.9 mil | Approximately 705 g/m² at Grade 100. | Magnetic thickness or stripping mass. |
Tests and the drawing call-out
Tests the document imposes
- Average coating thickness
- Individual specimen thickness
- Adherence
- Visual workmanship and freedom from uncoated areas
- Embrittlement where applicable
How to cite it
Drawing call-out
HOT-DIP GALVANIZE AFTER FABRICATION PER ASTM A123/A123M, MATERIAL CATEGORY <CATEGORY>, <MASKING AND REPAIR LIMITS>Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Finishes specified to ASTM A123
ASTM A123 — frequently asked
Does ASTM A123 have one minimum thickness?
No. The required grade depends on measured steel thickness and product category, ranging from 35 to 100 µm.
Is ASTM A123 intended for threaded fasteners?
Separate hardware and fastener standards such as ASTM A153 and ASTM F2329 are usually more appropriate. A123 is primarily for batch-galvanized iron and steel products and fabrications.
When should vent holes be added?
Before galvanizing, every sealed or overlapping volume needs safe venting and drainage. The galvanizer should review hollow fabrications before release.
ASTM A123 is copyrighted by ASTM International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗