Hello,

I wondered what were the most useful sizes of core drills to have?

I'm guessing something slightly bigger than 32mm, something slightly
bigger than 40mm, and something about 110mm? For both sizes of waste
pipe and 4" fan ducting, respectively.

Is that about right? What about any others?

Are 22mm and 28mm any use? Perhaps the22mm one for 15mm pipe sleeved
in conduit or overflow flow pipe and the 28mm one for 22mm pipe
sleeved in something (though I can't think what).

I'm wondering whether to return the silverline 22mm one I bought from
toolstation's clearance section. It fits the drill via a hex shaft
rather than an arbour, so you cannot use a pilot bit, which I think
reduces how useful it is.

Thanks,
Stephen.