The Jackson 20-330 series Grade 1 Overhead Concealed Closer is a certified ANSI/BHMA Grade 1 closer. The closer is manufactured in the U.S.A. under strict ISO 9001 guidelines and is designed to give the ultimate durability and maintenance free service. This closer is truly universal. One basic closer mechanism allows for single or double acting, center-hung or offset applications and is non-handed. Suitable for both interior and exterior installations, it provides complete door control in a compact and concealed design suitable for aluminum, glass, wood and hollow metal doors. Available in 4 fixed spring sizes with an optional adjustable hydraulic backcheck that will provide the ultimate protection from wind or violent door swings without impeding normal traffic flow.