- The KNAPP®️ Forstner Bit with Adjustable Depth Stop is specially designed to drill the perfect hole depth for the UNO 30 and DUO 30 and 35 Hook Connectors. This forstner bit is available in 30 mm and 35 mm and includes a custom adjustable depth stop that allows for a perfect connection every time wh using the UNO and DUO hook connectors. The tungsten carbide tipped blade ensures optimal protection for long-lasting performance. All of our KNAPP® drill bits and router bits are made in Austria and made of high-quality steel.