Chuck bungs are primarily used to block the centre of the chuck to stop swarf and coolant going down the spindle. The threaded hole which can be used for the removal of the bung can also be used for mounting a back stop.
FANUC 21i-T Control Max’ Turning Ø 320mm X Axis Travel 180mm Spindle Bore 52mm 12 Station Block Turret 7.5kW Spindle Motor Spindle Range to 3500rpm Tool Setting Arm Collet Chuck Machine Multifeed ML1 Barfeed Separate Transformer Electronic Handwhe...