These jump rings are made of anodized aluminium and are sold in bags of 100.  NOTE: These rings are slightly thinner than the other rings of this size due to an error in the anodo\izing process.
 
The wire thickness is 1.2mm and are available in a avariety of sizes - we measure the internal diameter (for example a 5/32 size will have an internal diameter of approx 4.1mm)