Casement window slide hinge arm (pair).
Note: The #24-EP and #24-ER are identical except that the #24-EP has a retainer clip on the end of the arm that attaches to the hinge track. These hinges are used on the newer models which slide in a track that is about 10″ long. Some of the 10″ tracks have a spring steel wire ring on the hinge track post and require the #24-ER hinge.