Sold each, priced each

Steel ball bearing roller
Adjustable steel housing assembly
Fits on Columbia, Keller and other sliding patio door manufacturers
JET PATIO DOOR - 1-1/2 Wheel , 13/16 Housing 
 

Manufacture: Production Enterprises, Hialeah, FL

Diameter: 1-1/2-inch
Housing Tab Style: Plain Back
Housing Width: 3/4-inch with dimples
Material: Steel
Roller Diameter: 1-1/2-inch
Roller Edge Type: Concave
Roller Material: Steel
Roller Width: 5/16-inch
Type: Concave
Width: 3/4-inch

Related parts:
13209 - Rollers only

Helpful Article: How to Replace Rollers in an Aluminum Sliding Glass Door