Abstract: A window actuator for a casement window has an actuator housing having a generally channel shaped receptacle portion defined by a rear wall, a front wall generally parallel to the front wall, and two end walls spaced to form therebetween a hollow interior with an open top surrounded by an outwardly extending peripheral flange and a base plate extending from the rear wall beyond the open top for mounting on a window frame. A worm housing is connected to and extends outwardly from the front wall of the housing and holds, by a plastics locking member threaded into the worm housing, a worm which is rotated by a manually actuable crank to drive a rotatable wheel mounted within the hollow interior. The wheel has an outwardly extending portion connected by an arcuate pivotal link to an actuator arm pivoted at its inner end on the base plate and arranged so that in the extended position of the arm, the link goes overcenter against a stop on the housing.