These coupling sockets are mounted on the motor shaft of the brush machine TW1901-P by means of Allen screws (T3). A coupling bush for the narrow brass brush is supplied as standard on the machine. These brushes have a pin (shaft) of 6 mm. If you want to use a wide brush, you need a different coupling bush because the pins of the wide brushes are thicker, namely 8 mm. Assembly is easy with an Allen key (supplied as standard with the machine).