Strut Channel Sizes: 1-5/8” vs 7/8”, What the Numbers Mean

Two sizes cover the vast majority of strut channel used in mechanical, electrical, and plumbing work: 1-5/8” and 7/8”. Both come slotted, both are dimensionally standard across manufacturers, and mixing them up on a materials list is one of the more common ordering mistakes on a job.

1-5/8” channel is the standard, heavy-duty profile. It’s what you reach for on pipe racks, cable tray support, multi-run trapeze assemblies, and anywhere the load adds up. If a spec just says “Unistrut” or “strut channel” without a size called out, 1-5/8” is the safer assumption.

7/8” channel, sometimes called “half-slot” or junior channel, is a lighter profile. It’s common on single conduit runs, small equipment mounts, and signage, where 1-5/8” would be overbuilt, and more expensive, for the job.

Reading the part numbers

Industry-standard part numbers (originally Unistrut’s own numbering, now used generically across manufacturers) tell you the profile and gauge at a glance:

Part #	Profile	Gauge
P1000	1-5/8” x 1-5/8”, slotted one side	12 ga
P3300	1-5/8” x 7/8”, slotted one side	12 ga
P4100	1-5/8” x 13/16”, slotted one side	14 ga
P5500	1-5/8” x 2-7/16”, slotted one side	12 ga
P1001	1-5/8” x 3-1/4” back-to-back (double), slotted both sides	12 ga

A lower gauge number means thicker steel, 12-gauge is thicker (and stronger) than 14-gauge. If your spec calls out a gauge, it’s worth checking it against the part number rather than assuming.

Which one do you need?

If you’re specifying for a job and aren’t sure, the safest default is 1-5/8” (P1000), the most common profile in the field and compatible with the widest range of brackets, clamps, and fittings. 7/8” is worth choosing specifically when weight and cost matter more than capacity margin, not as a default.