Your link is a Colt commercial link dating 1920’s - 1930’s for the Colt (Browning) aircraft guns.
The cal .30 Colt links are known at least blued, copper-washed and zinc-coated
The Colt aircraft guns were exported to numerous customers in different calibers during the inter-war period.
Hereafter a few exemples of Colt links for export. Note that only the cal .30 links have no mention of caliber whereas for the others, the caliber is added to the markings.
One can also note the the zinc-coated link for .50 aircraft guns marked with the Colt logo.