CLTR21U is a pair of 19-inch panel mounting rails providing 21U of rack space with 10-32 UNF tapped holes on typical EIA spacing. It is an optional mounting rail listed under the CLC Series colocation server rack cabinet program, making it a practical choice for data center and telecom technicians who need tapped-hole mounting instead of, or in addition to, the square-hole rails supplied with a cabinet bay.

The rails are formed from mild steel and finished in painted thin film black. Each rail carries white silkscreened U markings so installers can identify rack positions quickly when mounting or re-mounting equipment. The mounting dimension height is 36.75 in (933 mm), with an overall drawn length of 36.78 in (934 mm) covering 21U. Shipping weight for the pair is 6 lbs (2.72 kg).

Within the CLC Series, 21U is the rack space per compartment in the 2-bay cabinet configurations (CLC2B36BK, CLC2B42BK and CLC2B48BK), so CLTR21U matches a single 21U bay. A square-hole equivalent, CLSR21U, is offered alongside it, and the same rail family is available in 10U, 14U and 44U lengths for other bay layouts.

The part is manufactured in Canada, is USMCA compliant and TAA-compliant, and is RoHS and REACH compliant. Standards listed for this part number are cULus, PCI and TAA-compliant, under UL file number E474597. With 10-32 tapped holes, equipment mounts directly with 10-32 screws; mounting hardware is not included with CLC Series mounting rails.