Steel Roller Assembly with 1 inch Steel Roller for Sliding Screen Door. 
Roller Assembly consists of steel ball bearing wheel and adjustable diecast mounting bracket with stamped steel housing. 
These Roller can be right or left handed. 

Roller Edge Type: Concave 
Roller Material: Steel 
Roller Width: 3/8 Inch 
Roller Diameter: 1-Inch 
Priced and Sold in Pairs.

IMPORTANT NOTE:
Adjustment screw only turns one way, (clockwise) it works on a cam that increases and then drops back to a low position and starts over.
The bottom rollers should be adjusted first, the top rollers should be adjust enough so the screen does not jump off the track - do not overly tighten the top rollers.