Holders Holders for use with the Siemens 3SB3 round series of pushbuttons, selector switches and indicator lights. Available in metal or plastic The Siemens 3SB3 series is a range of plastic and metal commanding devices for front panel mounting and rear wire connection. The 3SBB3 series of pushbuttons, selector switches and indicator lights are of a modern industrial design with a flat construction and are easy to install.