Screw slot runner system

A suspension ceiling grid system comprising elongated runners formed with a bulb at their upper edge, a planar central web, and an open channel at their lower edge, said open channel being defined by lateral flanges extending in opposite directions from the lower edge of said web, a pair of laterally spaced, substantially parallel channel sidewalls, and inturned lips extending laterally toward each other from said sidewalls and terminating at spaced and opposed inner edges, said lips cooperating to define a longitudinal opening along the lower side of said channel, said grid system including first runners having end connectors adapted to connect with second runners at predetermined locations, said second runners providing notches in their channels at said locations, said notches extending through said lips and a first portion of the associated sidewalls adjacent to said lips leaving intact a second portion of said sidewalls and said flanges extending uninterrupted past said notch, said lips at the ends of said first runners and adjacent to the notches of said second runners being shaped to fit together to form a miter joint when said runners are interconnected, said second portions providing substantial resistance to buckling of said runners at said notches when lateral load are applied thereto.