Has anyone ever seen these before? If so any clue as to when they available?

Thanks!!

….trying to post pics….

Not sure what I was doing wrong, but couldn't get the pics to post properly...hopefully the link works.

Thought these were "interesting", as I had never seen these before. Searching the web, I found some ECHO branded scope mounts from the 50s-60s. The companies formal name was E.C. Herkner Co...hence ECHO. seems they also made some other shooting accessories so swivel studs seem like something the could have made, though I did not find a reference to such.

Just curious to know if any of the folks here remeber/have seen these...

Thank you, Baxter! The second pic shows the echo stamp..

I had some on a model 70

Interesting BT. Do you recall roughly what time period that may have been?