This is a S&W, Model 94 factory made long chain (chain is 30” long with 8-rings at the end). It is “A” marked and uses the “N” key.
These were made by the factory, for the Smith & Wesson salesman & staff that travelled with firearms in carrying cases. They were built to fit around the cases, hence the 8-adjustable rings, to secure the case from easy break-in at airports, shows, & shooting ranges. The sets were built in various lengths and designed with multiple rings on the chain so several sets could be attached for extra wide cases. I have a factory letter explaining there use, and I received this set from the S&W Historian and were one of the sets he used. His letters states that there were probably less than 100 sets ofthes manufactured.