4? Deep recessed channel to mount low voltage tape lights flush with surface. Field cuttable Aluminum extrusion Recessed installation Included: Diffused lens and end caps Length: 4? (field cuttable) Finish: Aluminum Compatible Tape Lights: NUTP1: 24V Standard LED Tape Light (Silicone Encapsulated) NUTP3: 24V RGB LED Tape Light NUTP4: 12V Standard LED Tape Light NUTP5: 24V Hy-Brite LED Tape Light NUTP6: 12V RGB LED Tape Light NUTP7: 24V Standard LED Tape Light NUTP8: 24V High Output LED Tape Light NUTP9: 24V Side-Lit LED Tape Light NUTP10: 24V CCT Color Tuning LED Tape Light NUTP11: 24V RGBW LED Tape Light NUTP12: 24V Comfort Dim LED Tape Light NUTP14: 24V COB LED Tape Light