The 5" length exists for fastenings where the fixture stack eats the embedment — doubled ledgers, thick furring over uneven block, stacked shim packs, and treated plates over rigid insulation. Subtract your full fixture thickness from the 5" length to find your working embedment, and plan on at least 1" of thread in the base material. If that leaves you short, step up to the 6" version; if you have more embedment than you need, the standard 1 1/4"–4" flat heads will cost less.
410 stainless suits exterior and high-moisture work and far outlasts plated carbon steel, but it is not a marine-grade alloy. For direct salt spray, splash zones or submerged work, use a 316 stainless concrete screw.
[ITEMPRICE]
