This is a European made reproduction German WW2 bicycle light blackout cover. They are made from a casting of an original part in a cold cast resin. The size is just under 8.5cm across. The cover attaches with 4 leaf prongs that would be on the outer edge of the cup of the light.  It is $6.50 to ship this item by registered airmail to anywhere outside Europe. Withing Europe the postage is $5.50.