A sliding shoe for a sliding/pivoting window having a shoe body which is of two piece construction. A cam trapped between the two portions of the shoe has a cam-shaped body, which rotates in complementary cam-shaped openings through the shoe portions to expand the shoe laterally, and a chamfered cam-shaped annulus which rotates in a complementary bevelled seat in the shoe body to expand the shoe in a direction perpendicular to the lateral expansion. The shoe is thus locked in position in the frame channel very early in the rotational cycle of the cam, and provide secure locking engagement against the sides, top and bottom of the channel when the sash is pivoted only slightly out of the plane of the frame.