Dome and thumbturn CH020 Does not contain an exterior lock piece. Thumbturn is covered by a plastic cover which can be broken in an emergency. To be used when turning a regular thumbturn into an emergency only thumbturn. Chrome surface treatment. Specifications Type of product Close Thumbturn CH021Exit thumbturn for solid doors. Replaces handles. Thumbturn CH005Thumbturn for balcony door latches. Thumbturn CH001Thumbturn for solid doors.