Looks familiar, but...

[Kiros32]

Found this in Suffolk at about 7 inches. I see no attachment points or holes. Any ideas?

 

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[Ant]

It looks like a expansion/freeze plug.

 

[Kiros32]

The raised dots in the middle; are they for decoration or do they serve a purpose?

 

[Charlie P. (NY)]

Reminiscent of the plate of a carbon microphone - but that could be coincidental.

 

[Ant]

Not that I know of, the other thing that came to my mind is a tire tube scuffer. If it is a freeze plug the marks have been transferred to the part by the die so that when it needs to be replaced a hole can be punched into it easily to pry out. Do you know what a freeze plug looks like? Hey I'm out in the desert looking at this on my cell phone.

 

[Ant]

Not sn expansion plug, I need to look on a monitor.

 

[Ant]

Okay made it home, got too hot anyway, are those stars knurling? That might be there to release the cap from the die after it was stamped. I think it looks like a dust cover/seal for the rear of an electric motor after looking at it on my montor. Does that ring a bell?

antique electric motor end cap - Google Search

 

[Kiros32]

Don't have it here at work, but what I can recall, the stars are knurling. I am not very familiar with electric motor end caps, but looking at the pictures, I don't see any that look similar. I think what I have it too shallow to be very effective as a dust cover. Plus, I see not holes or attachment points. I am quite stumped on this one, but I appreciate the effort Ant!

 

[Ant]

Okay your welcome. If it was a dust cap the flange could fit inside a holder like the setup in the first picture, the other photos are similar in my mind, good luck: