A2 Stainless Steel (ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70) is the most common stainless group for indoor and general outdoor fasteners. When flat head socket cap screws, unc are specified in this grade, the dimensions remain per ASME B18.3; the material determines corrosion behavior (good general corrosion resistance) 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 A2 Stainless Steel for Flat Head Socket Cap Screws, UNC
The most common stainless group for indoor and general outdoor fasteners. For flat head socket cap screws, unc, this matters when good general corrosion resistance is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Good general corrosion resistance |
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 A4 (316). 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
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 Flat Head Socket Cap Screws, UNC Available in A2 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 A2 Stainless Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
A2 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.
