This is from a Jennings "Mints of Quality" or Dutchboy slot machine. I don't know what else it's compatible for so please determine that yourself. But it you know what you're looking for, this should be easily identifiable.
This piece is attached below the underside of the mechanism floor, and is the housing for the sliding trap door and springs that create the "delay" pay portion. The sliding door and lever for it can be fabricated most likely.
Make me a reasonable offer. I paid over $100 for the entire mechanism, sold that way. So this is the extra piece. It's probably cheapest to ship this in a small USPS priority box which is about $7.70 I think.