ASTM F1941 / F1941M — electrodeposited coatings on threaded fasteners
The fastener-specific plating standard: how thread fit limits coating thickness, when de-embrittlement baking is required, how B850 and F1940 relate, and what to put on the order.
| Related service | Zinc Plating Cr3+ |
|---|---|
| Electroplating and coating | ASTM F1941 / F1941M |
| Also written as | ASTM F1941 (inch, UN/UNR), ASTM F1941M (metric), ASTM B850 (baking guidance), ASTM F1940 (process qualification) |
| Updated |
Scope — and what it does not cover
ASTM F1941 (inch, UN/UNR threads) and F1941M (metric) specify electrodeposited coatings applied to threaded fasteners: coating designation, the thickness a thread can accept while still gauging, embrittlement relief baking for hardened fasteners, and the tests used to verify thickness and adhesion. They do NOT set mechanical properties, do not cover non-electrolytic zinc flake (ASTM F1136) or hot-dip galvanizing (ASTM F2329), and do not guarantee corrosion life.
Standards are copyrighted documents. We explain scope, intent and practical application in our own words; obtain the current edition from ISO, ASTM, DIN or your national standards body.
What actually bites in production
- 1The thread governs. After coating, the fastener must still meet its thread limit — the GO gauge has to assemble — so the pre-plate thread is produced to leave room for the coating.
- 2Embrittlement relief baking is required at and above the hardness or strength trigger, commonly quoted as about 39 HRC or 1 000 MPa depending on the specification, and it starts promptly after plating.
- 3ASTM B850 is the companion guide for bake temperature and duration by strength. F1941 tells you when; B850 helps you decide how long.
- 4ASTM F1940 qualifies a plating PROCESS as non-embrittling. It is not a lot release test — ISO 15330 and ASTM F606 preloading tests examine actual lots.
- 5On nuts, the thread is tapped after plating or tapped oversize before plating. Decide which and write it down, or the assembly will not gauge.
Reference tables
Scroll the table sideways on a narrow screen.
Reference de-embrittlement bake window
| Strength / hardness of the fastener | Typical bake temperature | Typical minimum hold | Start after plating |
|---|---|---|---|
| ≤ 1000 MPa (≈ 320 HV / ≈ 31 HRC) | — | — | — |
| 1000–1200 MPa (≈ 320–375 HV) | 190–230 °C | 4 h | 1–4 h |
| 1200–1400 MPa (≈ 375–440 HV) | 190–230 °C | 8 h | 1–4 h |
| > 1400 MPa (> ≈ 440 HV) | 190–230 °C | 24 h | 1–4 h |
Typical reference values per ISO 4042 / ASTM B850 — the governing specification prevails. Baking is started as soon as possible; delay reduces its effect sharply.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
What to write on the drawing or PO
- Coating metal, thickness class and the supplementary treatment (passivation type, sealer), plus the significant surfaces.
- Thread designation and class before plating, with the statement that the fit must be maintained after plating.
- The baking requirement: temperature range, minimum hold, maximum delay after plating, and whether time-temperature records travel with the lot.
- Whether an embrittlement test (ISO 15330 / ASTM F606 preloading, or F1940 process qualification) is required, by whom, and on what sample size.
- The corrosion requirement as a separate line with method and hours.
What goes wrong when it is cited loosely
- Taking a thickness class from a general parts standard and applying it unchanged to a fine-pitch thread.
- Ordering plated class 12.9 socket screws without a written risk decision. Above roughly 390 HV many specifications forbid electroplating outright.
- Assuming the plater will simply know the baking parameters. Strength band, geometry and coating all change them, so they belong on the order.
- Treating a passed preloading test as proof that the shipped parts are safe. The parts that were tested were destroyed by the test.
Defects this standard gets cited on
Steel grades where this decision is made
Part types we process to this
Frequently asked questions
F1941 or F1941M — which do I cite?+
F1941 for inch (UN/UNR) threads, F1941M for metric. Citing the wrong one usually shows up as a thickness class that does not exist in the table you are reading.
How soon after plating must baking start?+
As soon as possible. Specifications commonly require parts to be in the oven within about 1–4 hours; the longer hydrogen sits in a stressed high-strength part, the less a bake can recover.
Do you bake in-house?+
Yes. De-embrittlement baking is run in our own ovens with logged time and temperature, and the record can be issued with the lot when the order calls for it.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
Related standards
Other standards in this reference
Send the drawing and let us check it against this standard
Send the drawing or the specification line as it is written today, the property class or coating requirement, the thread and tolerance class, and the part itself if you have one. We will tell you which lines are processable as written, which are arithmetically impossible on that thread, and what has to be added before the requirement can be quoted, inspected and defended.
We reply to quote requests within 24 hours.