Abstract: A tamper resistant fastener, which can only be rotated with a specific key, is described. The fastener includes a head for rotation about a vertical axis. The head is provided with the least two cutouts in the head of the faster spaced away from the vertical axis, the cutouts having a discontinuous sidewall. The side wall of each of the cutouts has a first generally vertical engaging surface for engagement by a mating member on a specific key for clockwise rotation of the head about the vertical axis and a second generally vertical engaging surface for engagement by the mating member on the specific key for counter clockwise rotation of the head about vertical axis. The side wall of the cutout is interrupted adjacent the second engaging surface to prevent engagement by a tool other than the specific key and thereby prevent rotation of the fastener in a counter clockwise direction by a tool other than the specific key.

Abstract: A tamper resistant fastener, which can only be rotated with a specific key, is described. The fastener includes a head for rotation about a vertical axis. The head is provided with the least two cutouts in the head of the faster spaced away from the vertical axis, the cutouts having a discontinuous sidewall. The side wall of each of the cutouts has a first generally vertical engaging surface for engagement by a mating member on a specific key for clockwise rotation of the head about the vertical axis and a second generally vertical engaging surface for engagement by the mating member on the specific key for counter clockwise rotation of the head about vertical axis. The side wall of the cutout is interrupted adjacent the second engaging surface to prevent engagement by a tool other than the specific key and thereby prevent rotation of the fastener in a counter clockwise direction by a tool other than the specific key.