Metallics JSS516516SS Screw 5/16-18 x 5/16 SKT S-Scr Cup 1 (Jar 100)

With a 5/16-18 thread and a 5/16 inch length, the screw is one diameter long, so in a tapped hole at least that deep it drives fully below the surface. That is what you want on a rotating collar or inside a lug pocket where a protruding screw would catch. If your tapped boss is shallower than 5/16 inch, the screw bottoms out before it clamps and you need a shorter length.

Yes, it is a stainless steel socket set screw, which is why it carries the SS suffix in the Metallics JSS516516SS part number. Stainless is the choice when the screw sits in a damp, outdoor, or wash-down location where a plain steel set screw would rust into the tapped hole.

They ship 100 to a jar. The jar pack is the usual MRO or van-stock quantity for a small fastener like this, so a single order covers a lot of repeat lug and collar work without loose-count bagging.

A cup point bites into the surface it clamps, leaving a small ring-shaped indent that resists the screw backing out under vibration. On electrical jobs that means holding a conductor in a mechanical lug, locking a collar or bus component on a shaft, or securing a fitting where you want permanent grip rather than a re-adjustable set. If you need to reposition the part repeatedly without marring it, a flat or nylon-tipped point is the better pick.

It's a socket (hex key) drive, so you need an Allen wrench, not a screwdriver. For a 5/16-18 socket set screw the hex socket is 5/32 inch, so a standard SAE hex key set covers it. There is no external head to grip, since the screw seats flush or below the surface of the hole.