A fastener apparatus (200) for a universal interface system (10) is disclosed. The fastener apparatus may include a body (160), an interior fastener (206), an exterior fastener (202), and a spring (204). The fastener apparatus may form part of an accessory for a universal interface system. The universal interface system may include an object (14) and an accessory (16). The object may include a mounting surface (124), a locking surface (126), and an elongated slot (22) extending from the mounting surface to the locking surface. The accessory may be fixed to the mounting surface. The universal interface system may include a ready configuration (258), a rotated configuration (262), and a locked configuration (266). The universal interface system further may include a released configuration (260), and a deployed configuration (264). The universal interface system may be used to secure accessories to a weapon.