A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When hex bolts are specified in this grade, the dimensions remain per ISO 4014 / ISO 4017; the material determines corrosion behavior (superior, including marine and chloride environments) and the service temperature range (approx. -200 °C to +400 °C, subject to the property class and the joint). Both are covered below with the size table.
Why Choose A4 Stainless Steel for Hex Bolts
Specified for marine, coastal and chemical applications. For hex bolts, this matters when superior, including marine and chloride environments is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Superior, including marine and chloride environments |
Galvanic & Galling Considerations
Two important notes for stainless hex bolts: (1) stainless can gall on stainless threads under load — use a thread lubricant or anti-galling compound, especially for M6 and below; (2) when joined to aluminum or galvanized steel, stainless can drive galvanic corrosion of the less-noble metal in wet service — isolate with a coating or sleeve where appropriate.
Comparable Grades
For Hex Bolts, the alternative stainless grade is A2 (304). Choose A2 (304) for general use and A4 (316) wherever chlorides are present; the molybdenum in A4 is the whole difference. Remember that stainless is the corrosion answer, not the strength answer — for load, look at class 8.8 or 10.9 instead.
Using Stainless Fasteners in Aluminum
Stainless steel is more noble than aluminum, so with an electrolyte present — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. Area ratio decides how bad it gets: a small stainless fastener in a large aluminum section is normally acceptable, a large stainless fastener in thin aluminum is not. Where the joint gets wet, isolate the metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of Hex Bolts Available in A4 Stainless Steel
| Size | Pitch coarse (mm) | Width across flats s (mm) | Width across corners e min (mm) | Head height k nom (mm) | Nominal diameter d (mm) | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| M1 | 0.25 | 2.5 | 2.71 | 0.7 | 1.0 | Below the ISO 4017 range (M1.6-M64); manufacturer series | Fully threaded |
| M1.2 | 0.25 | 3.0 | 3.28 | 0.8 | 1.2 | Below the ISO 4017 range (M1.6-M64); manufacturer series | Fully threaded |
| M1.4 | 0.3 | 3.0 | 3.28 | 0.9 | 1.4 | Below the ISO 4017 range (M1.6-M64); manufacturer series | Fully threaded |
| M1.6 | 0.35 | 3.2 | 3.48 | 1.1 | 1.6 | ISO 4014/4017 | Fully threaded |
| M2 | 0.4 | 4.0 | 4.32 | 1.4 | 2.0 | ISO 4014/4017 | Fully threaded |
| M2.5 | 0.45 | 5.0 | 5.45 | 1.7 | 2.5 | ISO 4014/4017 | Fully threaded |
| M3 | 0.5 | 5.5 | 6.01 | 2.0 | 3.0 | ISO 4014/4017 | Fully threaded |
| M4 | 0.7 | 7.0 | 7.66 | 2.8 | 4.0 | ISO 4014/4017 | Fully threaded |
| M5 | 0.8 | 8.0 | 8.79 | 3.5 | 5.0 | ISO 4014/4017 | Fully threaded |
| M6 | 1.0 | 10.0 | 11.05 | 4.0 | 6.0 | ISO 4014/4017 | Fully threaded |
| M8 | 1.25 | 13.0 | 14.38 | 5.3 | 8.0 | ISO 4014/4017 | Fully threaded |
| M10 | 1.5 | 16.0 | 17.77 | 6.4 | 10.0 | ISO 4014/4017 | Fully threaded |
| M12 | 1.75 | 18.0 | 20.03 | 7.5 | 12.0 | ISO 4014/4017 | Partial / fully threaded |
| M14 | 2.0 | 21.0 | 23.36 | 8.8 | 14.0 | ISO 4014/4017 | Partial / fully threaded |
| M16 | 2.0 | 24.0 | 26.75 | 10.0 | 16.0 | ISO 4014/4017 | Partial / fully threaded |
| M18 | 2.5 | 27.0 | 30.14 | 11.5 | 18.0 | ISO 4014/4017 | Partial / fully threaded |
| M20 | 2.5 | 30.0 | 33.53 | 12.5 | 20.0 | ISO 4014/4017 | Partial / fully threaded |
| M22 | 2.5 | 34.0 | 37.29 | 14.0 | 22.0 | ISO 4014/4017 | Partial / fully threaded |
| M24 | 3.0 | 36.0 | 39.98 | 15.0 | 24.0 | ISO 4014/4017 | Partial / fully threaded |
| M27 | 3.0 | 41.0 | 45.2 | 17.0 | 27.0 | ISO 4014/4017 | Partial / fully threaded |
| M30 | 3.5 | 46.0 | 50.85 | 18.7 | 30.0 | ISO 4014/4017 | Partial / fully threaded |
| M33 | 3.5 | 50.0 | 55.37 | 21.0 | 33.0 | ISO 4014/4017 | Partial / fully threaded |
| M36 | 4.0 | 55.0 | 60.79 | 22.5 | 36.0 | ISO 4014/4017 | Partial / fully threaded |
| M39 | 4.0 | 60.0 | 66.44 | 25.0 | 39.0 | ISO 4014/4017 | Partial / fully threaded |
| M42 | 4.5 | 65.0 | 71.3 | 26.0 | 42.0 | ISO 4014/4017 | Partial / fully threaded |
| M45 | 4.5 | 70.0 | 76.95 | 28.0 | 45.0 | ISO 4014/4017 | Partial / fully threaded |
| M48 | 5.0 | 75.0 | 82.6 | 30.0 | 48.0 | ISO 4014/4017 | Partial / fully threaded |
| M52 | 5.0 | 80.0 | 88.25 | 33.0 | 52.0 | ISO 4014/4017 | Partial / fully threaded |
| M56 | 5.5 | 85.0 | 93.56 | 35.0 | 56.0 | ISO 4014 | Partial / fully threaded |
| M60 | 5.5 | 90.0 | 99.21 | 38.0 | 60.0 | ISO 4014 | Partial / fully threaded |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this bolt in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Lengths and thread lengths outside the standard table are the commonest request, followed by a drive the standard does not offer and a head marked with your own part number. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
