Capitol Roller Assembly, Flat 1inch Steel Wheel

Part Number: 13301
Price: $9.50
Roller Assembly,
Flat 1inch Diameter Steel Wheel.
Used on old capitol doors, maybe the 350 or 950 series.
Sold each, Priced each 

Helpful Article:How to Replace Rollers in an Aluminum Sliding Glass Door
This product is similar to or the same as the following part numbers in these brands:
Prime-Line Products: D 1774
Strybuc Industries: 900-10138