The Series A, Class 2510 Type FW1, NEMA 4, watertight device, was obsoleted 1-14-2002 and was replaced with a Class 2510 FW1 Series B. Series B consists of a redesigned enclosure (box) and cover assembly. The new Series B is identical to the Series A except for the overall width of the enclosure (box) is slightly wider - wider by only .15`` (5/32``). The mounting holes for the Series B device are identical to the old Series A device. Important Note: Series A covers and boxes are NOT interchangeable with Series B devices due to the redesign. This is due to changes in location of the four (4) cover mounting screws.