1980-D RPM? 0

[Rick621]

Found this in some change, looks like an RPM. Couldn't find any documentation on this, or a value, if it is an RPM. Does anyone have any input?

[Fenntucky Mike]

Looks like mechanical doubling.

[Greenstang]

I agree, you can also see MD in the 1, 9 & 8 on the date.

[James Zyskowski]

Machine doubling 🤓

[Woods020]

Rick,

When you see a well defined “shelf” like is present here it is usually indicative of machine/mechanical/strike doubling (all the same thing). 
 

Some good material for learning the different types of doubling, and there are several, here is a good place to start. Understand that only very specific types of doubling are of interest as the rest are common occurrences in the manufacturing process. 
 

Machine Doubling:

http://www.error-ref.com/machine-doubling/
 

Doubled Die

https://www.error-ref.com/?s=Doubled+die

Die Erosion

https://www.error-ref.com/?s=Die+erosion

 

[Rick621]

Thanks for the info Woods020. Very informative.

[Mohawk]

I'm with the others.....definite machine doubling.