A twist lock for attaching a plastic shell of a thermal probe to a structural member such as a plastic intake manifold of an internal combustion engine in a socket in the structural member. The twist lock includes hooks on the plastic shell which traverse an annular shoulder at the bottom of the socket through notches in the shoulder when the shell is inserted in the socket and which are captured by the shoulder when the shell is rotated in the socket from an unlocked position to a locked position. The twist lock further includes a lug on the shell cooperating with a cam edge on a resilient lip around an open end of the socket to afford tactile representation of the progress of the shell toward and achievement of the locked position and to prevent reverse rotation of the shell from the locked position.