Button photocontrols (PBT) are compact, mounted inside protective enclosures such as fixtures or wiring boxes and have 3/8" dia threaded nipple with cell. Available in 120 or 208/240/277 volt models. Stem Mounted photocontrols (PTA) are weather proof and are mounted externally to fixtures or boxes. Stem is 1/2". Unit includes an adjustable light shield for sensitivity control.