Dura-Line Smooth Wall HDPE Innerduct Conduit. All Dura-Line's smooth wall conduit meets or exceeds one or more of the following standards: ASTM F-2160, ASTM D-3035, ASTM D-2239, ASTM D-3485, NEMA TC-7, UL 651, UL 1990, Bellcore GR-356. Smoothwall HDPE conduit is available in multiple nominal sizes (1/2"–6"), multiple reel put-ups (for 4" commonly 550', 766', 1000'), and is offered in black and other colors; factory pull tape is typically included on ≤4" reels (distributor-sourced data).