of the invention balance shoe 21 is also installed in main frame 12 during initial assembly sash 14 is positioned so that the pins 36 36 extending from arm 34 of pivot bar 22 are aligned with slots 64 64 and boss 56 is rotated to align keyway 58 with slots 64 64 pivot bar 22 is then pushed toward balance shoe 21 to engage arm 34 into the balance shoe 21 and thus lock the pivot bar 22 to the balance shoe 21 this is the condition of balance shoe 21 shown in fig1 15 as well as for example fig3 4 this would also represent sash 14 being in a window open condition with respect to main frame 12 after the window assembly has been mounted in place pivot bar 22 remains engaged with balance shoe 21 thereby permitting sash 14 to be rotated or pivoted from a completely closed condition where the locking components are shown in fig1 and 13 with tongue 74 engaged in notch 76 to an open position such as shown in fig3 4 and 14 15 during the rotation of sash 14 from the completely closed position the inclined walls of notch 76 function as a cam with respect to the inclined walls of tongue 74 to overcome the resilient engagement of the tongue in the notch and thus permit the boss 56 to be rotated to a condition where the tongue 74.