Crossbars are used to mount light fixtures to the electrical junction box. The adjustable all-purpose crossbar is used for mounting light fixtures to 3”, 3-1/4” or 4” electrical boxes. Kit Contents: 1 – All-Purpose Crossbar – Adjustable from 3 7/8” to 5”; 2 – 1/2" Mounting Screws; 2 – 3/4" Mounting Screws