B-Line B200SS4 Eaton series strut fittings and accessories, 1.62" Height, 1.62" Length, 1.62" Width, .18lbs, Steel, Square washer, Hole size 3/8 in diameter | Bolt size 5/16 in, Stainless steel type 304

It measures 1.62 x 1.62 x 1.62 inches as listed, so the bearing face is a 1-5/8 inch square. That footprint spans the open slot of standard 1-5/8 inch strut, which is why a square washer is used here instead of a round one: it bridges the channel lips rather than pulling through them.

Stainless steel, type 304. That is the grade normally specified for exterior and damp interior strut runs where plain or electro-galvanized hardware would rust at the washer face. For chloride-heavy service such as coastal or pool chemical rooms, a 316 fitting is the usual step up.

A round flat washer sized for a 5/16 bolt sits inside the strut opening and can pull down between the channel lips under load. The square B200SS4 measures 1.62 inches on a side, so it seats across both lips and spreads the clamp load onto the channel itself. Use it wherever you are bolting through the open face of strut rather than through a drilled hole in solid steel.

Yes. The listed bolt and thread rod size is 5/16 inch, so it works on 5/16 all-thread as well as 5/16 hex bolts. Pair it with a 5/16 nut; the washer is a bearing component only and no nut or bolt comes with it.