A4 Stainless Steel Flat Head Socket Cap Screws, UNC combine the dimensional form of ASME B18.3 with the material properties of grade ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80: superior, including marine and chloride environments, largely non-magnetic, service range approx. -200 °C to +400 °C, subject to the property class and the joint. This page summarizes the grade data, its corrosion behavior in service, the comparable grades, and the sizes supplied.
Why Choose A4 Stainless Steel for Flat Head Socket Cap Screws, UNC
Specified for marine, coastal and chemical applications. For flat head socket cap screws, unc, 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 flat head socket cap screws, unc: (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 Flat Head Socket Cap Screws, UNC, the alternative stainless grade is A2 (304). A2 (304) covers general indoor and outdoor service. A4 (316) adds molybdenum, which is what buys the chloride resistance for marine and de-icing-salt exposure. Where strength matters more than corrosion, plated alloy steel in class 8.8 or 10.9 is the swap to make.
Using Stainless Fasteners in Aluminum
The galvanic couple here runs the wrong way: aluminum is the less noble metal, so it corrodes and the fastener does not. What governs the rate is the ratio of areas — a large anode and a small cathode is a tolerable combination, the reverse concentrates the attack into thin material around the hole. An isolating washer plus sealant breaks the circuit; where that is impractical, match the fastener to the substrate.
Sizes of Flat Head Socket Cap Screws, UNC Available in A4 Stainless Steel
| Size | Pitch P (mm) | b (mm) | Head diameter dk (mm) | dk_mean (mm) | Head height k (mm) | r (mm) | Hex socket s (mm) | t (mm) | Length range l (in) | Reference standard |
|---|---|---|---|---|---|---|---|---|---|---|
| #0 | 0.318 | 6.096 | 3.505 | 3.239 | 1.118 | 0.076 | 0.889 | 0.635 | 1/16"~1 1/2" | ASME B18.3 |
| #1 | 0.397 | 7.417 | 4.267 | 3.95 | 1.372 | 0.093 | 1.27 | 0.787 | 1/16"~1 1/2" | ASME B18.3 |
| #2 | 0.454 | 8.738 | 5.004 | 4.636 | 1.626 | 0.109 | 1.27 | 0.965 | 1/16"~2 1/2" | ASME B18.3 |
| #3 | 0.529 | 10.058 | 5.74 | 5.321 | 1.854 | 0.126 | 1.575 | 1.118 | 1/8"~2 1/2" | ASME B18.3 |
| #4 | 0.635 | 11.379 | 6.477 | 6.007 | 2.108 | 0.142 | 1.575 | 1.397 | 1/8"~4" | ASME B18.3 |
| #5 | 0.635 | 12.7 | 7.137 | 6.617 | 2.286 | 0.159 | 1.981 | 1.549 | 3/16"~4" | ASME B18.3 |
| #6 | 0.794 | 14.021 | 7.798 | 7.239 | 2.464 | 0.175 | 1.981 | 1.676 | 1/8"~4" | ASME B18.3 |
| #8 | 0.794 | 16.662 | 9.119 | 8.509 | 2.845 | 0.208 | 2.388 | 1.93 | 1/8"~5" | ASME B18.3 |
| #10 | 1.058 | 19.304 | 10.439 | 9.779 | 3.226 | 0.241 | 3.175 | 2.21 | 3/16"~8" | ASME B18.3 |
| 1/4" | 1.27 | 25.4 | 13.487 | 12.84 | 4.089 | 0.318 | 3.962 | 2.819 | 3/8"~10" | ASME B18.3 |
| 5/16" | 1.411 | 31.75 | 16.662 | 15.951 | 5.029 | 0.397 | 4.775 | 3.429 | 1/2"~10" | ASME B18.3 |
| 3/8" | 1.587 | 38.1 | 19.837 | 19.063 | 5.944 | 0.476 | 5.563 | 4.039 | 1/2"~12" | ASME B18.3 |
| 7/16" | 1.814 | 44.45 | 21.438 | 20.637 | 5.944 | 0.556 | 6.35 | 4.039 | 3/4"~12" | ASME B18.3 |
| 1/2" | 1.954 | 50.8 | 23.825 | 22.987 | 6.375 | 0.635 | 7.925 | 4.369 | 3/4"~12" | ASME B18.3 |
| 5/8" | 2.309 | 63.5 | 30.175 | 29.21 | 8.23 | 0.794 | 9.525 | 5.588 | 3/4"~14" | ASME B18.3 |
| 3/4" | 2.54 | 76.2 | 36.525 | 35.471 | 10.058 | 0.953 | 12.7 | 5.588 | 1"~14" | ASME B18.3 |
| 7/8" | 2.822 | 88.9 | 42.875 | 41.808 | 11.887 | 1.111 | 14.275 | 6.299 | 1 1/2"~14" | ASME B18.3 |
| 1" | 3.175 | 101.6 | 49.225 | 47.993 | 13.716 | 1.27 | 15.875 | 7.544 | 1 1/2"~14" | ASME B18.3 |
| 1 1/8" | 3.629 | 114.3 | 55.575 | 54.191 | 15.519 | 1.429 | 19.05 | 8.255 | 1 5/8"~14" | ASME B18.3 |
| 1 1/4" | 3.629 | 127 | 61.925 | 60.376 | 17.348 | 1.587 | 22.225 | 9.093 | 1 5/8"~14" | ASME B18.3 |
| 1 3/8" | 4.233 | 139.7 | 68.275 | 66.561 | 19.177 | 1.746 | 22.225 | 10.211 | 1 3/4"~14" | ASME B18.3 |
| 1 1/2" | 4.233 | 152.4 | 74.625 | 72.758 | 21.006 | 1.905 | 25.4 | 11.049 | 1 3/4"~14" | ASME B18.3 |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Material and finish are usually what drives a special — a grade the standard part is not stocked in, or a coating chosen against a salt-spray figure instead of a default. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
