Metallics JFM39 6-32 x 5/8 in. Flat Head Slotted Machine Screws - Steel Zinc - Each

6-32 is the standard thread used for device mounting in outlet and switch boxes, and the Metallics JFM39 is a 6-32 UNC screw with 32 threads per inch cut to ANSI/ASME B1.1. At 5/8 inch long it gives extra thread engagement over the short screws that ship with devices, which is what you want when a box is recessed behind thick plaster or a mud ring. The flat head sits flush when the hole is countersunk.

The JFM39 is built to ASME B18.6.3-1998 for head and body dimensions and ANSI/ASME B1.1 for the UNC thread form, with material to AISI 1006-1022. Those are the figures to put on a submittal. Note it is not Buy American compliant and is not ARRA compliant, with country of origin listed as multiple, which matters on federally funded work.

Slotted drive, so a flat blade screwdriver. The slot is 0.039 to 0.048 in. wide and 0.024 to 0.038 in. deep, which is a shallow, narrow slot typical of a #6 screw. Pick a blade that fills the slot and drive it by hand or at low speed; slotted heads have no self-centering feature and a fast impact driver will skate out of the slot and chew the head.

The JFM39 is rated at 550 lb minimum tensile strength, with hardness of Rockwell B70 to B100, made from AISI 1006 to 1022 low carbon steel. That is ample for mounting devices, plates, straps and small brackets. It is not a structural or high-strength fastener, so for anything carrying real suspended load use a graded bolt instead.

Zinc plated steel is a mild corrosion coating meant for dry indoor use. The JFM39 is steel with a zinc finish, which is fine inside panels, boxes and equipment rooms. For wet locations, exterior work, or anywhere washdown or salt air is in play, go to a stainless machine screw of the same 6-32 x 5/8 size instead.

A machine screw has a straight, uniform machine thread (here 6-32 UNC) and needs a mating tapped hole or a nut; it will not cut its own thread. The JFM39 is the right choice where the hole is already tapped, as in a device box ear, a panel, or an enclosure boss. If you are fastening into untapped sheet metal with only a pilot hole, you need a self-tapping sheet metal screw instead.

They come in a jar of 100, and 100 is the order minimum. The jar weighs 0.273 lbs. Handy for a van or a shop drawer where you are pulling a few at a time rather than opening a bulk box.

Metallics lists them for the electrical, plumbing, heating and air conditioning industries, and the zinc yellow finish is common in electronics work. In practice that means device and plate mounting, strap and clamp attachment, control panel and enclosure hardware, and general MRO fastening where a 6-32 tapped hole is involved.