Anyone know what is this?

[dso17]

found this part, not sure what is comes off?

[silverton_ford]

Ford Pickup 1961-1966 door pocket.   I think it was an option or it came with the Custom Cabs.  Not exactly sure how you would get one, but if the truck didn't have one there was a large plate that blocked off the hole in the door.

https://www.bobdrake.com/FordItem.aspx?Item=C5TZ-8120130&ReturnURL=/3472c65d-6c45-4025-bc38-24febf69f575&Category=3472c65d-6c45-4025-bc38-24febf69f575