A2 Stainless Steel Hex Head Cap Screws, UNC combine the dimensional form of ASME B18.2.1 with the material properties of grade ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70: good general corrosion resistance, 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 A2 Stainless Steel for Hex Head Cap Screws, UNC
The most common stainless group for indoor and general outdoor fasteners. For hex head 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 hex head 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 Hex Head 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
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 Hex Head Cap Screws, UNC Available in A2 Stainless Steel
| Size | b (mm) | Pitch P (mm) | c (mm) | dw (mm) | Width across corners e (mm) | Head height k (mm) | r (mm) | Width across flats s (mm) | Length range l (in) | Reference standard |
|---|---|---|---|---|---|---|---|---|---|---|
| 1/4" | 19.05 | 1.27 | 0.406 | 10.557 | 12.832 | 4.366 | 0.37 | 11.113 | 3/8"~12" | ASME B18.2.1 |
| 5/16" | 22.225 | 1.411 | 0.406 | 12.065 | 14.665 | 5.556 | 0.423 | 12.7 | 1/2"~12" | ASME B18.2.1 |
| 3/8" | 25.4 | 1.587 | 0.406 | 13.573 | 16.498 | 6.35 | 0.476 | 14.287 | 1/2"~12" | ASME B18.2.1 |
| 7/16" | 28.575 | 1.814 | 0.406 | 15.081 | 18.331 | 7.541 | 0.529 | 15.875 | 3/4"~12" | ASME B18.2.1 |
| 1/2" | 31.75 | 1.954 | 0.406 | 18.098 | 21.997 | 8.731 | 0.635 | 19.05 | 3/4"~12" | ASME B18.2.1 |
| 5/8" | 38.1 | 2.309 | 0.406 | 22.622 | 27.496 | 10.716 | 0.794 | 23.812 | 3/4"~14" | ASME B18.2.1 |
| 3/4" | 44.45 | 2.54 | 0.406 | 27.146 | 32.996 | 12.7 | 0.953 | 28.575 | 1"~14" | ASME B18.2.1 |
| 7/8" | 50.8 | 2.822 | 0.406 | 31.671 | 38.495 | 14.684 | 1.111 | 33.337 | 1 1/2"~14" | ASME B18.2.1 |
| 1" | 57.15 | 3.175 | 0.406 | 36.195 | 43.994 | 17.066 | 1.27 | 38.1 | 1 1/2"~14" | ASME B18.2.1 |
| 1 1/8" | 63.5 | 3.629 | 0.406 | 40.719 | 49.493 | 19.05 | 1.429 | 42.862 | 1 5/8"~14" | ASME B18.2.1 |
| 1 1/4" | 69.85 | 3.629 | 0.406 | 45.244 | 54.993 | 21.431 | 1.587 | 47.625 | 1 5/8"~14" | ASME B18.2.1 |
| 1 3/8" | 76.2 | 4.233 | 0.406 | 49.768 | 60.492 | 23.019 | 1.746 | 52.388 | 1 3/4"~14" | ASME B18.2.1 |
| 1 1/2" | 82.55 | 4.233 | 0.406 | 54.292 | 65.991 | 25.4 | 1.905 | 57.15 | 1 3/4"~14" | ASME B18.2.1 |
| 1 3/4" | 95.25 | 5.08 | 0.406 | 63.341 | 76.99 | 29.369 | 2.223 | 66.675 | 2"~14" | ASME B18.2.1 |
| 2" | 107.95 | 5.644 | 0.406 | 72.39 | 87.988 | 34.131 | 2.54 | 76.2 | 2 1/2"~14" | ASME B18.2.1 |
| 2 1/4" | 120.65 | 5.644 | 0.406 | 81.439 | 98.987 | 38.1 | 2.857 | 85.725 | 2 1/2"~14" | ASME B18.2.1 |
| 2 1/2" | 133.35 | 6.35 | 0.406 | 90.487 | 109.985 | 42.069 | 3.175 | 95.25 | 3"~14" | ASME B18.2.1 |
| 2 3/4" | 146.05 | 6.35 | 0.406 | 99.536 | 120.984 | 46.038 | 3.493 | 104.775 | 3"~14" | ASME B18.2.1 |
| 3" | 158.75 | 6.35 | 0.406 | 108.585 | 131.982 | 50.8 | 3.81 | 114.3 | 3 1/2"~14" | ASME B18.2.1 |
| 3 1/4" | 171.45 | 6.35 | 0.406 | 117.634 | 142.981 | 55.562 | 4.128 | 123.825 | 3 3/4"~14" | ASME B18.2.1 |
| 3 1/2" | 184.15 | 6.35 | 0.406 | 126.683 | 153.979 | 58.737 | 4.445 | 133.35 | 3 3/4"~14" | ASME B18.2.1 |
| 3 3/4" | 196.85 | 6.35 | 0.406 | 135.731 | 164.978 | 63.5 | 4.763 | 142.875 | 4"~14" | ASME B18.2.1 |
| 4" | 209.55 | 6.35 | 0.406 | 144.78 | 175.976 | 68.263 | 5.08 | 152.4 | 4"~14" | ASME B18.2.1 |
Dimensions are independent of the material: every size above is available in A2 Stainless Steel.
Custom manufacturing · Made to drawing
Need this bolt 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 hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
