Reverse-threaded aluminum coupler. Tapered threads accommodate a wide range of conduit ODs within a given conduit size. Also available in a Riser/Plenum rated version.
Features
Self-threading, which draws each end of the conduit into the center of the coupler
Not air-tight or water-tight
Threads may reduce conduit ID
Wide tolerance 'universal' versions available for many corrugated duct sizes
The Riser/Plenum versions are approved for use in both Riser and Plenum applications – Riser UL 1666 & Plenum UL 2024