Stainless Steel Options: 304, 316, and 316L
Last updated September 27, 2026
Stainless steels are iron alloys with at least about 10.5 percent chromium. The chromium forms a self-repairing oxide layer on the surface, which is what stops the steel from rusting. OpusFab lists two stainless grades for CNC machining, 304 and 316, plus 316L for metal 3D printing. This guide explains what each is for.
304: the general-purpose grade
304 (often called 18/8, for roughly 18 percent chromium and 8 percent nickel) is the most common stainless in the world. It has good corrosion resistance, welds well, and is food safe.
Use 304 for enclosures, brackets, kitchen and lab equipment, and general hardware that sees moisture.
316: the corrosion-resistant grade
316 adds 2 to 3 percent molybdenum, which improves resistance to chlorides: saltwater, de-icing salts, and many chemicals. It is often called marine grade and is common in marine hardware, medical devices, and chemical processing equipment.
It machines much like 304 and costs more. If a part will live near salt water or aggressive cleaning agents, 316 is the safe choice.
316L: the metal printing grade
316L is the low-carbon variant of 316, offered for metal 3D printing (DMLS/SLM) rather than CNC machining. Printed 316L parts are fully dense and corrosion resistant, and suit complex geometries that machining cannot reach, such as internal channels and consolidated assemblies. Printed parts can be up to 420 x 420 x 450 mm. See Metal 3D Printing (DMLS/SLM).
Grades not currently listed
Two common stainless grades are not in the editor at the moment:
- 303: the free-machining stainless, with added sulfur for fast cutting. A good fit for high-volume turned parts like fittings and fasteners.
- 17-4 PH: a precipitation-hardening stainless that can be heat treated to very high strength, roughly 1,170 MPa yield in the common H900 condition.
If your part needs one of these, request a custom quote and the team will confirm availability.
Quick comparison
| Grade | Process | Corrosion resistance | Typical uses |
|---|---|---|---|
| 304 | CNC | Very good | General hardware, enclosures |
| 316 | CNC | Excellent | Marine, medical, chemical |
| 316L | Metal 3D printing | Excellent | Complex printed parts |
When stainless beats aluminium
- Thin or small features that must not bend or wear. Stainless is far harder and stiffer than aluminium.
- Wear surfaces and threads that see repeated use or sliding contact.
- Elevated temperatures where aluminium softens.
- Corrosive environments where you do not want to rely on a coating.
- Food, medical, and hygiene applications.
When aluminium wins
Aluminium is about one third the density of stainless and much faster to machine, so aluminium parts are usually lighter and cheaper. Unless you need stainless for one of the reasons above, 6061-T6 aluminium is the more economical choice.
Stainless parts on OpusFab can be ordered Raw (As-Machined), bead blasted, powder coated, or PVD coated. The Surface Finishes Overview explains what each finish does.