Control knobs on nearly all equipment are fitted to a round shaft with a flat section - D shape.
They're nearly always just pushed onto the shaft and held firm by a spring clip - some knobs are held in place by a small grub screw but seldom if ever on a cooker I suspect.
Just try pulling off your broken knob.
Buy a replacement - e spares perhaps or directly from Belling maybe - and push it on.
Good luck...
Portnoy, September 2014
