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 low 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 Low Head Socket Cap Screws, UNC
The most common stainless group for indoor and general outdoor fasteners. For low 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 low 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 Low Head Socket Cap Screws, UNC, the alternative stainless grade is A4 (316). The practical dividing line is chlorides: A2 (304) is fine until salt is involved, and A4 (316) exists for the cases where it is — coastal, marine and road-salt service. Neither reaches the strength of a plated class 8.8 or 10.9 fastener.
Using Stainless Fasteners in Aluminum
Expect the aluminum to corrode, not the fastener — stainless sits higher in the galvanic series, so the aluminum is the one that gives up material. A small fastener in a thick section spreads the loss over a large area and is usually fine; a large fastener in thin sheet concentrates it and is not. Keep water out of the joint, or isolate the two metals with a nylon or coated washer and a sealant.
Sizes of Low Head Socket Cap Screws, UNC Available in A2 Stainless Steel
| Size | Pitch P (in) | b (in) | Head diameter dk (in) | Head height k (in) | C_max (in) | J (in) | T (in) | K (in) | r (in) | Length range l (in) | Reference standard |
|---|---|---|---|---|---|---|---|---|---|---|---|
| #4 | 0.025 | 0.448 | 0.18 | 0.056 | 0.009 | 0.05 | 0.038 | 0.008 | 0.006 | 1/8"~4" | ASME B18.3 |
| #5 | 0.025 | 0.5 | 0.203 | 0.062 | 0.012 | 0.062 | 0.044 | 0.008 | 0.006 | 3/16"~4" | ASME B18.3 |
| #6 | 0.031 | 0.552 | 0.224 | 0.069 | 0.013 | 0.062 | 0.05 | 0.008 | 0.007 | 1/8"~4" | ASME B18.3 |
| #8 | 0.031 | 0.656 | 0.268 | 0.082 | 0.014 | 0.078 | 0.06 | 0.008 | 0.008 | 1/8"~5" | ASME B18.3 |
| #10 | 0.042 | 0.76 | 0.309 | 0.095 | 0.018 | 0.094 | 0.072 | 0.008 | 0.009 | 3/16"~8" | ASME B18.3 |
| 1/4" | 0.05 | 1 | 0.372 | 0.124 | 0.025 | 0.125 | 0.094 | 0.01 | 0.013 | 3/8"~10" | ASME B18.3 |
| 5/16" | 0.056 | 1.25 | 0.434 | 0.155 | 0.033 | 0.156 | 0.11 | 0.01 | 0.016 | 1/2"~10" | ASME B18.3 |
| 3/8" | 0.062 | 1.5 | 0.559 | 0.187 | 0.04 | 0.188 | 0.115 | 0.01 | 0.019 | 1/2"~12" | ASME B18.3 |
| 7/16" | 0.071 | 1.75 | 0.622 | 0.218 | 0.047 | 0.219 | 0.135 | 0.015 | 0.022 | 3/4"~12" | ASME B18.3 |
| 1/2" | 0.077 | 2 | 0.747 | 0.249 | 0.055 | 0.25 | 0.151 | 0.015 | 0.025 | 3/4"~12" | ASME B18.3 |
| 5/8" | 0.091 | 2.5 | 0.871 | 0.311 | 0.07 | 0.312 | 0.25 | 0.015 | 0.031 | 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. Where the standard stops, the drawing takes over: fine pitches, left-hand threads, partial threading, and property classes above the catalogued grade where material and heat treatment allow. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
