A hole diameter of 25mm to 32mm is suitable for fitting the 7" tap and 30mm to 34mm is suitable for 8" wooden taps. A 38mm to 44mm diameter hole is suitable for fitting a 10" tap.
I was delighted with my barrel, which was of infinitely superior quality to any other barrels I had managed to source locally. It is water tight as advertised (much to my surprise). It was also an extremely reasonable price. Mrs Ryan, Herefordshire.