I would think being used as a shim between the striker and the jamb it would not be threaded, if a similar looking plate were used as a backing plate/stiffener inside the pillar it would be threaded. I only had my drivers side apart to undo some prior cobbling and can't remember if they were threaded.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy