The Manfrotto 046MC Expan Drive with Metal Chain (Gray) is a Background paper drive set for one roll with chain which incorporates two expandable core units. One side has a large toothed gear to affix a metal link chain, allowing convenient raising and lowering of the background paper roll. The other side has an adjustable tension drag. These double core units are unique in that when the overall screw on which the drive unit is mounted is tightened the drive expands from a minimum of 1.8" to 2" (46mm to 78mm) . It accommodate cored paper rolls in any length, all you need to do is insert the Expans at both ends, and tighten up until they're snug and then mount the entire assembly on your background holder hooks.