Card Style Medical Gas Pipe Markers conform with the NFPA 99 2018 Health Care Facilities Code and CGA C-9 2013 Standard Color Marking of Compressed Gas Containers for Medical Use. Self-Adhesive Medical Gas Markers were designed to wrap completely around pipes ranging from 3/8" through 2" in diameter. Size M2, one 4" x 7" card. We recommend you use size M2 on pipes from 1" to 2" in diameter. Size M3 to be used on pipes ranging from 3/8" through 3/4" in diameter. These are adhesive backed markers that you peel and stick, all markers include arrows.