These are used in many places on the playfield to hold plastic posts down. Usually, they screw into a t-nut.
Used in these games and more:
BALLY
BLACK ROSE, CREATURE FROM THE BLACK LAGOON, DR DUDE, DR WHO, GILLIGANS ISLAND, HARLEY DAVIDSON (Bally), PARTY ZONE, TWILIGHT ZONE, WORLD CUP SOCCER 1994
WILLIAMS
FUNHOUSE, INDIANA JONES, STAR TREK THE NEXT GENERATION, TERMINATOR 2,