This Harmony ZBY legend holder has black or white background and is marked with "O" lettering. It is compatible with Harmony XB4, XB5 and XB7 push buttons and pilot lights. This legend holder allows you to customize the control unit with an engraved tag, in line with the design approved by your customer. It is compatible with any standard 22mm Harmony control or signalling unit. It provides clear and resilient symbol marking on the label, with high contrast.