Screw material and finish picker
Same size, very different behaviour. Pick by where the screw lives, not by price.
| Material | Strength | Corrosion | Magnetic |
|---|---|---|---|
| Stainless A2 (304) | Roughly grade 70 | Very good indoors and in fresh water | Mostly non-magnetic |
| Stainless A4 (316) | Roughly grade 70 | Excellent, handles salt water | Mostly non-magnetic |
| Carbon steel, black oxide | Grades 8.8 / 10.9 / 12.9 | Poor — rusts if it gets wet | Yes |
| Zinc-plated steel | Usually 4.8 or 8.8 | Fair indoors | Yes |
| Brass | Low | Good, will patina | No |
| Titanium | High for the weight | Excellent | No |
| Nylon / polymer | Low | Immune | No |
Stainless A2 (304)
The default for anything that might see moisture. Galls if you drive it fast and dry.
Stainless A4 (316)
Boats, coastal installs, pool equipment, anything chlorinated.
Carbon steel, black oxide
What is inside most laptops and machines. The black finish is cosmetic, not real protection.
Zinc-plated steel
Cheap general hardware. Fine in a dry cabinet, not outdoors.
Brass
Used where you need no sparks, no magnetism, or a soft screw that will not damage a housing.
Titanium
Bikes, drones, camera rigs. Expensive and it galls badly without anti-seize.
Nylon / polymer
Electrical isolation and PCB standoffs. Never for anything structural.
Two traps worth knowing
- Galvanic corrosion: a stainless screw in a bare aluminium part will eat the aluminium in damp conditions. Isolate it or use a matching material.
- Galling: stainless and titanium can cold-weld to each other when driven fast. Go slow and use a little anti-seize on anything you may need to remove.
Gear for this job
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A2 stainless screw assortment
The default for most repairs
A4 / 316 marine stainless screws
Salt air, pools and outdoor mounts
Nylon and brass screws
Non-conductive and non-magnetic jobs