2 Pack, High tension steel spring roller assembly fits onto the Columbia Uni-Fit series door. This roller assembly has a 1 in. high density polyethylene roller mounted in the housing. The flat steel spring end catches onto the inside of the door frame while the flat edges of the two tabs extending out in front of the roller restrict the roller from retracting too far up into the door frame as it rolls. This sliding screen door roller assembly insert has a thinner high density polyethylene frame than the Prime-Line part B 646. It has an adjustable high density polyethylene inner housing and high density polyethylene roller. The assembly inserts into the bottom or top of the sliding screen door using the included screws. The roller adjusts to the correct position needed. This style is found on Columbia sliding screen doors but is also used on a variety of other sliding screen door manufacturers. Please note dimensions and design when comparing with old roller.