Metallics JHSF51634SS Screw 5/16-18 x 3/4 Hx Hd Serr Flang (Jar 100)

No. The serrated flange under the hex head spreads the bearing load like an integral washer, and the serrations bite into the mating surface to resist loosening from vibration. That's one less loose part to handle overhead. If the surface is soft, coated, or you don't want the finish scored, use a plain hex bolt with a washer instead, since the serrations will mar the material.

100 pieces per jar. Metallics packs it as a jar rather than a bulk box, which is what makes it practical to keep on a service van or in a shop bin for strut and enclosure work. Order quantities are in jars, so one unit is 100 screws.

Yes, it's a stainless screw, which is why it gets specified for damp, exterior, and washdown locations where a plain steel fastener would rust and seize in the thread. Pair it with stainless channel nuts or stainless hardware where you can, since mixing stainless with plain zinc-plated steel in a wet location puts the plated part at a disadvantage galvanically.

5/16-18 is the common thread for strut and channel hardware, so this size is what goes into channel nuts and spring nuts when hanging conduit straps, trapeze supports, cable tray, and enclosure brackets. Metallics catalogues the JHSF51634SS as an electrical fastener for exactly that work. At 3/4 inch it's sized for fastening a strap or bracket flange to channel, not for through-bolting thick assemblies.

It's coarse thread. 5/16-18 is the UNC pitch for that diameter; the fine (UNF) version would be 5/16-24. So it runs into standard 5/16-18 UNC nuts, channel nuts, and tapped holes, and it will not engage a 5/16-24 hole. Check the nut marking if you're mixing stock from different bins.