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to those who offered to look in 'stock' to see if they has a spare knob to fit.My Powerfix electronic digital caliper suggests the following:
Shaft (D shaped) external diameter 6mm Knob recess internal diameter 38mm - although a sub-38mm knob would be fine.
I broke the knob on the temperature control and moved the selector knob across but it would be nice to easily select between off, cold, half and full power.
Cheers
Dave R