| Bolt | F2329 Hot Dip Galvanizing | B695 Mechanical Galvanizing | F1136 Zinc/Aluminum (Geomet) | F2833 Zinc/Aluminum |
| A325 | Approved | Class 55 | Grade 3 | Grade 1 |
| F1852 | Not Approved | Class 55 | Not Approved | Not Approved |
| A490 | Not Approved | Not Approved | Grade 3 | Grade 1 |
| F2280 | Not Approved | Not Approved | Not Approved | Not Approved |
| *Other coatings may be used on 120ksi/A325 fasteners upon agreement between the purchaser the and the user. Coatings on 150ksi/A490 fasteners must be qualified by ASTM committee F16. *F1136, F2833, and F3019, as of 2020, have been withdrawn and combined into a new coating standard, F3393. |
Plain
A plain bolt, as you may have guessed, is a bolt with no coating. This is also commonly referred to as a black bolt. You will also hear people call these bare, plain, or plain finish.
While some confusion may arise due to the term black bolt as there are other coating options that
provide a true black finish like black oxide or black zinc. However, these are so uncommon in the construction fastener industry it’s rare for those coatings to be used.
F2329 Hot Dip Galvanizing
Hot dip galvanizing is the most common form of coating. Galvanize bolts refer to a bolt with a corrosion-resistant zinc coating. Different from zinc-plated bolts, galvanized bolts have the zinc fused to the steel at a molecular level.
For galvanized bolts to meet this specification they must pass certain tests. These tests are coating thickness, finish and appearance, embrittlement test, and adhesion test.
The only grade of F3125 bolt allowed to be hot dip galvanized is the A325-1.
B695 Mechanical Galvanizing
Different from hot dip galvanizing where the bolts are dipped into molten zinc, mechanical galvanizing is the process of cold-welding zinc to the bolt. In order to do this the parts being galvanized are deposited in a spinning drum with various chemicals, zinc powder, and glass beads. These beads then cold-weld the zinc-powder onto the surface of the product.
The B695 specification covers the requirements in the process of coating bolts with zinc mechanically. Only the seven thickest classes are referred to as mechanically galvanized.
The only bolts allowed to have this coating are A325-1 and F1852.
| Class | Minimum Thickness, μm |
| 110 | 107 |
| 80 | 81 |
| 70 | 69 |
| 65 | 66 |
| 55 | 53 |
| 50 | 50 |
| 40 | 40 |
| 25 | 25 |
| 12 | 12 |
| 8 | 8 |
| 5 | 5 |
Class 55 is the most common class used for ASTM fasteners and is roughly the same thickness as hot dip galvanizing per ASTM F2329. 53μm is equivalent to 0.002087 inches or 2.087 mils.
F1136 Zinc/ Aluminum (geomet)
This specification covers what is known as zinc plating. Zinc plating is pretty straightforward, it is the process of coating a bolt in zinc. This can be done by dip-spinning, dip-draining, or spray methods.
The F1136 specification is an ASTM requirement for the basic requirements and testing methods for zinc plating.
This method of applying a corrosion-resistant coating is not as durable as other methods such as hot dip galvanizing and is commonly used for aesthetic purposes. The grades of F3125 bolts allowed to have these coatings are A325-3 and A325-3.
F2833 Zinc/ Aluminum
The only difference between this ASTM specification and F1136 is this specification is for A325-1 and A490-1.