TheÂ Manfrotto 046MC Expan Drive with Metal ChainÂ incorporates two expandable core units. One side has a large toothed gear to which a metal link chain affixes, permitting convenient raising and lowering of the background paper roll. The other side has an adjustable tension drag. The 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 46 to 78mm. To accommodate cored paper rolls in any length, all you do is insert the Expans at both ends, tighten up until they're snug and mount the entire assembly on your background holder hooks.