This is a Stantel part number 8121M1000472KX, which is a single pressure differential switch. It is used for controlling the pressure in a single system by opening and closing a contact when the pressure differential reaches a set point. The features of this part include: a brass body construction, a 1/2 inch NPT connection, adjustable differential settings, a manual reset and weatherproofing. The temperature range of this switch is -40 C to 140 C and it has an UL rating of CSA C22.2 No.205. It is suitable for use in oil, air, water, or other non-corrosive media.