# Drill hole size for a given screw size in tile

I need to install a grab bar in a ceramic-tiled shower. I plan on drilling through the tile and screwing into studs (no anchors) with stainless steel screws.

I know I need to use a carbide or diamond bit, but what I'm wondering is, what size hole should I make for a given screw size, given that ceramic tile obviously doesn't have the "give" that wood has. For example, if you drill a smaller pilot hole, is there a risk that the screw will crack the tile as it's screwed in? On the other hand, if you drill a hole the same size as the screw, then perhaps there won't be any contact between the screw and tile, and the bar won't be as "secure"?

• The hole in the tile will not secure the screw. Make the hole the max diameter of the screw, no bigger, no smaller. Any tiny difference will not matter, a half inch hole for a 1/8 screw might. May 1 at 21:50
• "perhaps there won't be any contact between the screw and tile, and the bar won't be as "secure"?" - properly tightened, there will be plenty of contact between the face of the tile and the flange of the bar. The tile will be squeezed against the stud and that's what holds it all up. May 2 at 5:11
• Your screw is holding the mounting bracket of the grab bar to the wood. The tile is held to the wall by the mastic. There should be no impact from the screw on whether or not the tile stays on the wall. May 2 at 12:54

You want the hole through the tile a tiny amount larger in diameter than the outside diameter of the screw body. If the hole in the tile is smaller than the screw the tile will most likely crack as the screw in inserted or the screw will bind and twist off.

Drill your pilot hole for the screw into the stud after the hole through the tile is completed.

• Thank you. Just to confirm, when you say "outside diameter of screw body," do you mean including the threads (thread diameter), or no?
– yroc
May 1 at 22:31
• If nothing behind the tile except air, then the screw body/threads should past right though without any force May 1 at 22:35
• @yroc - including the threads. The screw should not touch the tile. May 2 at 8:53

I discovered small diamond hole saws a few years ago. (Milwaukee Diamond MAX or similar, starting at 3/16".) The SWMBO likes to get decorative flower pots, but some of them lack drains or the drains are plugged with glaze. The hole saws make quick work of adding drainage without shattering the delicate crockery.

Do find a spare tile to practice on. I start with the drill tipped slightly and a very low speed until it creates a groove, then slowly square the bit up and increase the speed. (The start is so slow that I can use a finger against the side of the bit to keep it from "walking".) A little water for coolant improves the lifespan of the bit.

The diameter of the bit should provide a clearance hole for the screw, i.e. slightly larger diameter than the O.D. of the screw. (Hole saws tend to make slightly oversize holes) Stop as soon as you complete the hole through the tile, bedding and backer board and switch to a standard twist drill for the smaller pilot hole in the stud.

The risk of cracking the tile is largely a matter of whether there is a gap between the back of the tile and the framing. It ought to have backer board installed tight to the framing and the tile bedded without gaps. There is no need to overtighten the screws, just run them down until they're snug.

NB: Don't forget to caulk thoroughly during installation. Water in walls is evil.