ASTM F2329/F2329M Hot Dip Zinc Coating for Fasteners

Stud Bolts, Nuts, Screws, Threaded Rod & Washers

ASTM F2329/F2329M specification covers the requirements for hot-dip zinc coating applied to carbon steel and alloy steel bolts, screws, washers, nuts, and special threaded fasteners. It also provides for minor coating repairs. Nails and rivets are not included in this specification.
It is intended to be applicable to fasteners that are centrifuged or otherwise handled to remove excess galvanizing bath metal (free zinc). The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

ASTM F2329/F2329M Material & Manufacturing Process

Condition of the as received Fasteners
Received Fasteners-The fasteners as received by the galvanizer shall be free from contaminants that are not readily removed in the cleaning process and would adversely affect the galvanizing.
Unless otherwise covered in this specification, all processing parameters shall be in accordance with the requirements of Specification A153/A153M.
Process Control
Galvanized fasteners subjected to a process control plan based upon batch lot level shall comply with the batch lot sampling plan in Table 1, and the sampling plan for production lot (prevention process) as determined in 10.2.2 shall be applied.
Process Control of Batch LotA Sampling Plan
Batch Lot Size Sample SizeB
Average Coating ThicknessC Adhesion AppearanceD
5 to 25 1 1 1
26 to 50 1 1 2
51 to 150 2 1 2
151 and over 2 2 2
  • (A) The acceptance criterion in all cases is zero defects.
  • (B) The sample size is the number of specimen(s) required to be tested/inspected to the applicable criteria.
  • (C) Frequency of coating thickness measurements: one set of specimen(s) for every five batch lots. For test method.
  • (D) Visual inspection for conformance.
Spinning and Quenching
Parts shall be spun immediately following removal from the galvanizing bath and quenched in water. In addition, small parts shall be air cooled, as needed, in order to prevent the formation of zinc oxide. Parts, which cannot be spun shall be brushed or handled otherwise to remove the excess zinc.
Alteration of Threaded Fasteners
Fasteners that have been hot-dip galvanized shall not be further altered (such as subjected to a cutting, rolling, or finishing-tool operation) the galvanizer unless specifically authorized in writing the purchaser. Hot-dip galvanizing of externally threaded fasteners shall meet the thread fitting requirements of the specified product standard or specific allowance as determined the customer. NOTE 1: The scope of this specification does not cover the requirements regarding the overtapping of galvanized nuts. These requirements are established the applicable product standard, such as Specification A563, Specification A563M (or others), or in writing the purchaser, if needed.
Secondary Processing
When requested the purchaser, treatments such as chromating or phosphating shall be applied to reduce the possibility of wet storage staining (white corrosion) or to assist subsequent painting. When specified on the purchase order, the nuts, bolts, or screws shall be lubricated to enhance assembly.
Touch-up and Repair
Bare, cut, or damaged spots found on fasteners after galvanizing, totaling less than 1% of the coated surface area, may be repaired with paints containing zinc dust. Such paints shall have zinc-dust concentrations of 65 to 69% or concentrations above 92% in the dried film. The repairing party shall select the paint and follow its application instructions. The applied coating shall provide barrier protection, and preferably be anodic to steel. Thickness measurements of repaired areas shall not be required. NOTE 2: Experience shows that, in general, organic zinc-rich systems are tolerant of marginal surface preparation and are not critical of climactic or atmospheric conditions for curing. Corrosion resistance and service performance are very dependent on the properties of the paint system, the extent of surface preparation, and the skills of individual applicators.

ASTM F2329/F2329M Coating & Dimensional Requirements

Coating Thickness
The zinc coating thickness shall meet the requirements of table below. See Supplementary Requirement S1 when specifying coating thickness for fasteners meeting the requirements of Specification A394.
Zinc Coating Thickness
DimensionA,B Minimum Thickness on Surface
Average Thickness of All 
Specimens Tested 
(Production Lot)C,B
Average Thickness of All 
Specimens Tested 
(Batch Lot)D,B
Average Thickness of 
Individual SpecimenB
Fasteners and nuts over 3/8 in. [M10] in diameter 
Washers 3/16 in. [4.7 mm] and over in thickness
0.0020 in. [50 μm] 0.0017 in. [43 μm] 0.0017 in. [43 μm]
Fasteners and nuts 3/8 in. [M10] and under in diameter 
Washers under 3/16 in. [4.7 mm] in thickness
0.0017 in. [43 μm] 0.0015 in. [38 μm] 0.0015 in. [38 μm]
  • (A) In the case of long pieces, such as anchor rods and similar articles over 5 ft [1.5 m] in length, the thickness measurement shall be determined at each end and the middle of the article. In the case of a fully threaded rod, the thickness measurements shall be determined at each end of the article. In no case shall the average of the measurements be below the average thickness shown in the Average Thickness on Individual Specimen column. The number of specimens to be tested per order shall be as specified in Section 10. Note-Based upon mathematical calculations, 1.0 oz /ft2  [305 g/m2] of zinc surface corresponds to an average coating thickness of 0.0017 in. [43 μm].
  • (B) Inch-pound and SI units may not be exact equivalents.
  • (C) In no case shall the average reading of a single specimen be below the average thickness shown in the Average Thickness on Individual Specimen column.
  • (D) See Test Methods and Process Control of Batch LotA Sampling Plan Table. In no case shall the average reading of a single specimen be below the average thickness shown in the Average Thickness on Individual Specimen column.
The dimensional characteristics of the fasteners shall be in accordance with the requirements of the purchaser, when specified in the order. The purchaser shall ensure that the effect of the heat generated the galvanizing process is compatible with the fastener regarding the final dimensional characteristics of the parts. Furthermore, the galvanizer shall not be held responsible for any unanticipated distortion of parts. In addition, the purchaser shall provide fasteners having sufficient dimensional allowance to accommodate the zinc thickness deposition.
Adhesion of Zinc Coating
The zinc coating shall adhere tenaciously to the surface of the base metal. The method for testing the condition

ASTM F2329/F2329M Testing Methods

Tests shall be made to ensure that the zinc coating is being furnished in accordance with this specification and as specified for the following :

Coating Thickness
Average Coating Thickness on an Individual Specimen - To calculate the average coating thickness of one specimen, a minimum of five readings shall be taken. In case the geometry of the specimen does not permit five readings, five test specimens shall be used to establish the average reading. The determination of the coating thickness shall be made on a portion of the fastener that does not include any threads in accordance with Practice E376. In case of arbitration, the thickness of coating shall be determined cross section and optical measurement, in accordance with Test Method B487. Thus, the thickness determined is a point value. No less than five measurements shall be made at locations on the test specimen, which are as widely dispersed as practical, so as to be representative of the whole surface of the test specimen. The average of those selected measurements is the average coating thickness.
Finish and Appearance
Finish and appearance shall be visually inspected.
Embrittlement Test
If the product standard requires testing for hydrogen embrittlement of galvanized fasteners, testing shall be done in accordance with Test Methods F606/F606M or other test method(s), as required the purchaser.
Adhesion Test
Testing for adherence shall be conducted as determined in the section on Adherence of Specification A153/A153M.