Cap of some sort?

[Bharpring]

This cap has a date on it July 13 1869 and the letters "OK" as well. Does anyone know what it could have been used for?

 

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[longcut]

Just a wild guess ....... In my early years , my grandmother had a soda bottle with a hole in the cap to sprinkle water on clothes while she was ironing them ..... I don't know what the cap was used for originally ...........

 

[TheCannonballGuy]

The date is almost certainly a United States Patent issuance date. You could do some research through the Patents issued on that date, and find out what your mystery cap is, and what it was used for.

In doing my own research on civil war era Patents, I found the "average" number of Patents issued on any particular day in the 1860s was usually about 30... so that's not TOO many you'll have to search through. Look for your cap (or disc) in the illustrated diagram which accompanies most Patents. Here's an example of a Patent diagram... note that the parts are labeled, and explained in the Description section of the Patent.

 

[Anduril]

The date is almost certainly a United States Patent issuance date. You could do some research through the Patents issued on that date, and find out what your mystery cap is, and what it was used for.

In doing my own research on civil war era Patents, I found the "average" number of Patents issued on any particular day in the 1860s was usually about 30... so that's not TOO many you'll have to search through. Look for your cap (or disc) in the illustrated diagram which accompanies most Patents. Here's an example of a Patent diagram... note that the parts are labeled, and explained in the Description section of the Patent.

My math says about 138 patents on average -- keeping in mind that patents are only issued once a week (or thereabouts).

Here's a pretty good resource to narrow down a timeline when only the patent number is known, assuming it's a US patent:
https://www.uspto.gov/web/offices/ac/ido/oeip/taf/issuyear.htm