Are these screws adequate for securing a 304 stainless steel shelf bracket?

Question

I have a bunch of 304 stainless steel shelf L brackets, they are thick brackets, ~6 gauge steel (5mm). They have 5 holes, long side has 3, and the short side has 2. All are 5mm in diameter, though they came with no fasteners.

The problem is that a screw should be 2 3/4 in (2.75 in) minimum length, to be strong in the stud, correct? I have plaster and lath walls, and I think they are slightly thicker than standard drywall.

What the hell can I do? The longest M5 Metric lag is 60mm, (2.3622 inches).

What should I do? How should I secure the the bracket to the stud in the wall? What about securing the bracket to the shelf? Keep in mind this is stainless, so that means using fasteners that won't corrode fastening something stainless.

Answer 1

Typically, 1-1/2" (about 40mm) is plenty in a wooden stud (properly piloted). It's rare that I'd go much deeper since you increase the risk of damaging electrical cables, which are centered at about 1-3/4" (45mm). Keep in mind that the holes punched in such brackets give you a clue as to their intended load range. If they were super heavy duty brackets they'd have larger fastener holes.

Three such fasteners will hold a heck of a lot of weight. (For extreme loads, the long side goes on the wall.) Penetrating deeper may increase pullout strength, but if you're loading the shelves that heavily, pullout isn't your primary concern. Crushed plaster and fastener bending will occur first.

I don't know what you'd use into the shelf since I don't know what your shelves are.