Spec Sheet Preview: The Alpha Communications® / TekTone OH19_ series flush backbox/housings are made of heavy gauge galvanized steel. They are designed to be used with the OH19_ series aluminum panel frames. These backboxes/housings are used with a variety of apartment entry intercom and video intercom lobby panel modules, as well as specialty and annunciator modules. Electrical knockouts are provided on the top, bottom and back of these units.