[Bob Bidonde]

Hi Werner,
Measure the diameter of a real GAV knob. Measure the diameter of the GAV knob in the picture. Compare the two diameters and note the difference. Measure the diameter of the accessory in the picture. Add or subtract the difference in GAV diameters to your measurement of the accessory's diameter. Looking at the picture, I guess that the diameter of the accessory is larger the the GAV knob.