Viking Quick Response Extended Coverage Concealed Horizontal Sidewall Sprinkler VK638 is a thermosensitive spray sprinkler pre-assembled with a threaded adapter for installation with a domed cover. The glass bulb operating element and special deflector characteristics meet the challenges of quick response extended coverage standards. The cover plate provides up to 1/4” (6.35 mm) of horizontal adjustment and is available with several decorative finishes to meet design requirements. The two-piece design allows installation and testing of the sprinkler prior to installation of the cover plate. The “push-on”, “thread-off” design of the concealed cover plate assembly allows easy installation of the cover plate after the system has been tested and the finish work has been completed. The cover assembly can be removed and reinstalled, allowing access behind the surface of the wall without taking the sprinkler system out of service or removing the sprinkler.