The Rollerblade Lightning Memory Buckles are sold in a pair and come in one size. The buckles are for both the cuff AND middle buckle (45-degree) positions for Rollerblade Lightning Skates.

The Rollerblade Lightning Memory Buckles allow for quick and easy entry with a consistent fit. Once adjusted, you never need to set again to get that same fit. Just latch and skate!
 
This buckle is considered to have standard middle buckle (SMB) mounting, but not standard cuff buckle (SCB) mounting as it mounts at one point on both sides.

Standard Middle Buckles (SMB). Two-point mount buckles or straps that mount at one point on each side.  SMB buckles and straps are compatible across different brands and models using this same mounting method.
 
Standard Cuff Buckles (SCB) mount at two points on the buckle side, and one point on the receiver side. So this would not be a SCB.