Available in metric sizes, GN 129.2 Steel and Stainless Steel Hinges are used for doors that are flush with frame on outside. Once assembled, they cannot be unhinged. Being mounted from inside, hinges are especially suitable for doors and trap doors that must not be detachable from outside as anti-tamper device. Hinges are available in steel, with zinc-plated, blue passivated finish; American Standard Series 303; or American Standard Series 316.