of the bottom flange 30 of the cross tee 14 39 abuts the vertical side edge 90 of the bottom flange 28 of the main beam at this point the end of the top bead 38 of the cross tee 14 39 engages the side of the top bead 36 of the main beam and on the opposite side of the main beam the protrusion 46 on the upper tab 42 engages the web 24 of the main beam 12 likewise providing a three point rigidly braced secure connection of this cross tee to the main beam in sliding the right end of the cross tee 14 39 downwards the gap initially existing vertically between the upper and lower tabs has become extinguished the lower surface of the upper tab now is juxtaposed upon the upper surface of the lower tab and the gap has shifted to being between the upper tab 42 and the prong 70 nothing needs to be bent or irreversibly clicked together or riveted or otherwise extraneously fastened in order to form the tight secure level joint at 16 the right end of the cross tee 14 39 can be disconnected from the main beam 12 at the joint 16 by a reversal of the procedure just described then the left end of the cross tee 14 can be disconnected from the main beam 12 at the joint 16 the embodiment shown in fig4 8 has come to be the preferred embodiment because its structure is modified to permit either cross tee to be connected to and disconnected from the main beam at the same joint without requiring connection.