And yes, the obvious answer is 3/16" … that doesn't work.
I'm installing a towel rod and hook in a bathroom that is fully tiled. The instructions with the rod & hook both said to drill a 3/16" hole for the included anchors, so I bought a Rigid 3/16" diamond tile drill bit. Drilling the first two holes went great, until I tried to fit the anchor in. Didn't fit.
Generally with drywall, the anchor is a little bigger than the hole, and you just force it in and it works fine. There's no give with the tile though.
For reference, I grabbed a caliper and started measuring things. 3/16" is 0.1875" The holes I drilled with the 3/16" bit are actually 0.225" and the widest part of the anchor is 0.245" — almost 1/4"!
As a secondary question — assuming I get get the right size bit — am I going to run into trouble trying to make these holes larger? If so, is there a better way you can think of to mount the hook with the two 0.225" holes I already have?
Best Answer
If you are wary of making the holes larger (which is possible and as Tester101 says just make the hole in the tile larger) then you could just go for a smaller anchor and screw.
Obviously this will depend on whether the smaller screws are still a good fit for the holes in the hook. Also the load the hook can take might be reduced, but as you're not going to be swinging from it (hopefully!) you should be OK.