This is the Hot Racing M3 Medium Aluminum Standoff Spacer Set, including 16 total spacers. 

Specifications:
Outside diameter of standoff: 5.8mm (.23 inch)
Inside diameter of Standoff: 3.1 mm (.12 inch)

Includes:

• (4) 2mm thick spacers
• (4) 4mm thick spacers
• (4) 6mm thick spacers
• (4) 8mm thick spacers