Metallics JSSMSS44 Screw M4 x 8 SKT S-Scr Cup St-Blk (Jar 100)

It's an M4 x 8 socket set screw with a cup point, in black steel. The M4 is the metric thread diameter and the 8 is the length in millimeters, so it drives with a hex key through the internal socket rather than an external head, and the cup point bites into a shaft or mating part to hold it against rotation.

Each jar holds 100 of the M4 x 8 cup point socket set screws. The jar pack is how these are sold, which suits a service van or a bench drawer where small metric set screws get consumed a few at a time.

An M4 socket set screw takes a 2 mm hex key in the standard metric pattern. There is no external head to grip, so the screw seats flush or below the surface of the collar or hub it is threading into, and a worn or undersized key will round out the socket.

Cup point is the general purpose choice and what the JSSMSS44 is. The hollowed ring of the cup digs slightly into the shaft, which gives strong holding on parts that are not going to be repositioned often. Use a flat point instead when you need to clamp against a hardened or already machined surface without marring it, or where the part has to slide and be reset. Cone point goes into a drilled or spotted seat for permanent location.

The JSSMSS44 is black steel, which is a plain oxide type finish rather than a plated or stainless one, so treat it as an indoor and dry location fastener. Damp or exposed work calls for a stainless or zinc plated set screw instead.

Order it as Metallics JSSMSS44. That one number covers the M4 x 8 socket set screw, cup point, black steel, in the 100 piece jar.

Yes, they are carried as an electrical fastener. Small M4 socket set screws of this kind are the type used to lock set collars, lugs, clamps and mounting hubs on electrical assemblies, and the jar of 100 is sized for that repeat replacement work.