Metric copper washers. 
Grade 110 high purity copper.
M6 - 6mm Inside x 12mm Outside x 1mm Thick
M8 - 8mm Inside x 14mm Outside x 1.00mm Thick
M10 - 10mm Inside x 16mm Outside x 1.0mm Thick
M12 - 12mm Inside x 16mm Outside x 1.0mm Thick
M12 - 12mm Inside x 18mm Outside x 1.5mm Thick
M14 - 14mm Inside x 20mm Outside x 1.5mm Thick
M16 - 16mm Inside x 20mm Outside x 1.5mm Thick
M18 - 18mm Inside x 24mm Outside x 1.5mm Thick
Sold as a pack of 10.