and looking at the upper cross member 52 thereof there is located slidably therein a latch member 81 same is preferably made from a molded plastic material for example a self lubricating plastic such as nylon said latch member 81 is illustrated separately in fig9 for clarity and comprises a latch portion 82 and a slide portion 83 said slide portion 83 has a handle extension 84 which returning to fig1 extends through an opening in the upper cross member 52 for engagement thereof by an operator resilient means 89 are further provided for constantly urging said latch member 81 laterally outwardly beyond the periphery of said lower sash member in this embodiment although these details are not an essential part of the invention the handle extension 84 fig6 and 12 is on a portion of a slide member 85 having prongs 86 thereon which latter project through openings such as openings 87 or 88 depending upon the alignment of the parts for engaging the latch member 81 the resilient means 89 may be of any convenient form constantly urging the latch member 81 laterally outwardly and in this embodiment consists of a spring which bears at its rightward end as appearing in fig9 and 12 against a downwardly projecting abutment 95 fig1 a similar upwardly projecting abutment being shown at 91 in fig9 and is held at.