Metallics JG5HSF51658 Bolt 5/16-18 x 5/8 Ind Hx Hd Serr (Jar 100)

Indented hex head, serrated. The head is an indented hex (driven with a 5/16-18 series hex wrench or socket rather than a screwdriver) and the underside of the head carries serrations that bite into the mating surface to resist loosening from vibration. That makes it a one-piece fastener, so no separate lock washer is needed.

100 pieces, supplied in a jar. The jar pack is the usual format for shop and service-van stock, where you are pulling a handful at a time for strut, enclosure, and panel work rather than buying by the box for a single run.

For electrical work where the joint sees vibration, the serrated-flange style saves a part and a step: the serrations under the head do the anti-loosening job a split lock washer would. Pick a plain bolt and washer instead when the mating surface is a finished or painted panel you do not want scored, since the serrations are meant to dig in. On bonding and grounding connections that bite is usually wanted, not avoided.

At 5/8 inch under the head, this is a short bolt sized for thin-material joints, think sheet metal enclosure panels, strut fittings, and bracket-to-channel connections where only a nut or a tapped hole of a few threads is being engaged. Stack up your material thickness plus the nut height first; if that exceeds about 5/8 inch you need a longer 5/16-18 bolt instead.

Metallics part number JG5HSF51658. That one number covers the complete jar of 100 in the 5/16-18 x 5/8 indented hex head serrated configuration, so there is no separate size or finish option to specify on the order.