The 139S is sized for 3-inch trade size conduit and is used on rigid, IMC, and EMT runs. It is a single trade size only, so a 2-inch or 4-inch run needs the matching size strap instead, not this one.

A click-on strap like the SEPCO 139S snaps onto the conduit first, then fastens through a single hole to the surface. A two-hole strap needs two fasteners aligned on either side of the conduit. On long repetitive runs the one-hole click-on cuts the fastener count and the alignment work in half; two-hole straps are the choice where you want the extra bearing point against movement.

The 139S is zinc plated steel, which gives corrosion and rust resistance for general commercial and industrial exposure, including moisture contact on walls and structural framing. Zinc plating is a surface coating though, so for continuously wet, coastal, or chemically aggressive areas most electricians step up to stainless or PVC-coated supports.

Yes. The 139S provides the single mounting hole; the fastener is chosen to suit the surface, so you supply it. Wood or metal framing takes a screw, concrete or block takes an anchor, and strut mounting takes a strut nut and bolt. Order the anchors with the straps so the run does not stall.

The 139S is intended for conduit support on walls, ceilings, and structural framing. On overhead 3-inch runs the weight of the raceway plus conductors is the governing factor, so the anchor into the deck or framing has to carry the load and the spacing between straps has to follow the support interval your code requires for the raceway type.