Related Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Hot-Dip Galvanized F436 Washers per ASTM F2329
ASTM F2329 is the dedicated hot-dip galvanizing specification for ASTM F436 hardened steel washers and associated F3125 high-strength structural bolting. F2329 governs centrifuged hot-dip zinc coating to deliver corrosion protection without introducing hydrogen embrittlement or distorting the F436 hardness band. This page documents the F2329 coating thickness, mating-bolt compatibility, and post-galvanizing inspection requirements that TorqBolt applies to all F436 galvanized washer orders.
Why F2329 instead of A153 or B695
| Coating standard | Scope | F436 compatibility |
|---|---|---|
| ASTM F2329 | Hot-dip zinc coating for hardened fasteners (F3125, F436) | Yes (mandatory for HDG F436) |
| ASTM A153 / A153M | HDG for iron and steel hardware, general | Not preferred for hardened fasteners; F2329 supersedes |
| ASTM B695 | Mechanical zinc deposit (mechanical galvanizing) | Yes (alternative to HDG; no high-temperature exposure) |
| ASTM B633 | Electrodeposited zinc on iron and steel | Not for hardened structural; H2 embrittlement risk |
F2329 was created specifically to address two problems with applying general HDG (A153) to high-strength fasteners: (1) the dip temperature can over-temper the hardened bolt and washer reducing strength, (2) thread tolerance after dipping is hard to control. F2329 mandates centrifuging the parts immediately after withdrawal from the zinc bath and tighter coating-thickness control to keep threads gauge-able.
F2329 coating thickness for F436
| Parameter | F2329 requirement |
|---|---|
| Average coating thickness, min | 1.7 mils (43 microns) |
| Minimum local coating thickness | 1.4 mils (36 microns) |
| Thickness measurement method | Magnetic per ASTM E376 or microscopic cross-section |
| Number of measurement points | 3 per washer, on the bearing face |
| Coating adherence test | Knife-and-stripping per F2329 Section 7 |
| Embrittlement check | Bake at 250 +/- 25 deg F for 4 hours within 4 hours of plating; verify Charpy V-notch energy preserved |
Mating bolt-washer-nut HDG system
Galvanized F436 washers should be ordered as part of a complete HDG assembly: F3125 Grade A325 hot-dip galvanized bolt per F2329 + F436 hot-dip galvanized washer per F2329 + A563 Grade DH or DH3 over-tapped hot-dip galvanized hex nut. The nut must be over-tapped to accommodate the zinc-coated bolt thread; standard 2B class thread will not assemble.
| Component | Coating spec | Notes |
|---|---|---|
| F3125 A325 bolt | F2329 HDG | Class 2A thread before coating (tighter than standard) |
| F436 hardened washer | F2329 HDG | Same dip lot as bolt + nut for color match preferred |
| A563 DH heavy hex nut | F2329 HDG | Over-tapped per ASME B18.2.2 Note 6 (class 6H+oversize) |
| Lubricant on nut | Beeswax or proprietary HDG lube | Reduces galling during installation; F3125 ships pre-lubed |
Type 1 vs Type 3 HDG behavior
Galvanizing Type 1 (plain carbon steel) F436 washers is the typical case; the zinc coating gives the atmospheric corrosion resistance the carbon steel does not have on its own. Type 3 (weathering steel) F436 washers are NOT typically galvanized because the weathering chemistry depends on direct atmospheric exposure to develop the protective patina; coating prevents the patina from forming. For Type 3 service, use the bare Type 3 washer; for general HDG service, use Type 1 + F2329 coating.
Cross-references
For Type 1 carbon steel washer details see F436 Type 1 washers; for Type 3 weathering see F436 Type 3 washers. Dim tables across both types and all four shapes are on F436 washer dimensions. The companion structural-bolt torque chart with HDG K value adjustments is on F436 tightening torque chart.
Frequently asked questions
Can I hot-dip galvanize F436 washers per ASTM A153?
ASTM A153 covers general HDG of iron and steel hardware but is not the preferred standard for hardened structural fasteners. ASTM F2329 was created specifically for F3125 high-strength bolting + F436 hardened washers and includes the centrifuge, thickness-control, and embrittlement-test requirements that A153 lacks. RCSC Specification references F2329 (not A153) for galvanized F3125 / F436 assemblies. If a project specification cites A153 for the fasteners, request a change to F2329 before order release.
What coating thickness does F2329 require?
F2329 requires a minimum 1.7 mil (43 micron) average coating thickness measured on the bearing face of the washer, with no individual local reading below 1.4 mil (36 micron). Thickness is measured by magnetic gauge per ASTM E376 or microscopic cross-section. The 1.7 mil minimum balances corrosion-protection life against thread fit-up margin; thicker than 2.5 mil starts to compromise A563 over-tapped nut assembly.
Can Type 3 weathering F436 be galvanized?
It can be galvanized but should not be in most applications. The Type 3 weathering chemistry develops a protective rust patina during direct atmospheric exposure. Hot-dip zinc coating prevents the patina from forming and chemically isolates the weathering steel from the atmosphere. For bridges, transmission towers and exposed structural steel that intentionally weather to a controlled patina, specify Type 3 bare. For general HDG corrosion protection, specify Type 1 + F2329 coating.
Does galvanizing affect F436 hardness?
F2329 includes a hardness re-check after coating; the dip temperature of 840 to 850 deg F is below the F436 minimum tempering temperature (typically 1000 deg F+) so the hardness band of 38 to 45 HRC is preserved through HDG processing. The 4-hour bake at 250 deg F immediately after coating drives off any absorbed hydrogen and prevents delayed hydrogen embrittlement. TorqBolt's F2329 mill cert lists pre-coating and post-coating hardness side by side to document the unchanged result.
Satisfaction Survey
