What size drill bit to use for pilot whole?


18 Jan 2007
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United Kingdom
I want to drill into a solid wood door some hanging knobs.

What size drill bit should I use?

I really tiny one?
And then force the screw in?

Or one that is just a bit smaller than the screw?
How do I best judge the correct width?

Or... should I not bother and just drill into the wood?
When I've done this (for other things) for cheap wood like bits of Ikea furniture... it's come out bulging - same with tiny pilot hole.

ALSO... any comments about putting up the same hanging knob onto a hollow wood door?
Should I not bother as sooner or later it will come off?

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Door should not need piloting for screws, do you mean coat hooks , not familiar with the term ‘ hanging knobs’?
Hollow doors are unsuitable for fixing too.
thanks for the reply. this is what i have:

let me know what you think.
(meant for bathrooms. i thought would be OK for my solid wood door)
Can't see how you could hang a towel on those unless you sew a hanging cord in the corner of the towels.
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As said, modern screws have sharp points which generally do away with need for pilot holes, but if you drill one probably best to make it a couple or three mm less than the screw gauge.

Hollow door fixings are available if you want to google them.

How do I best judge the correct width?

Measure it with digital calipers. Or check it by eye by holding the pilot and screw in line with each other.

The "major diameter" in green is just the normal/nominal size of the screw. The measurement between the red arrows is the "root diameter". Your pilot drill should match the root diameter.


it's come out bulging

That happens when the pilot is too small (or no pilot at all). The screw then starts acting like a drill bit, pulling material out, rather than driving the screw forward.
I was taught to always drill pilot holes. I found out the importance of this when being lazy screwing a length of timber to a cupboard front -- it started to split where the screw was forcing the wood grain apart.

Drill bits are designed specifically to drive out material as mentioned above. Screws don't do this.
forcing the wood grain apart.

That's another important issue. When screwing wood to wood, a 'clearance hole' is as important as the pilot hole. For example, screwing plywood to timber with a number 8 screw...

  1. Drill 3mm pilot hole, full length of the screw
  2. Drill the countersink
  3. Drill 4.5mm clearance hole, just the depth of the plywood (be warned, it will try and pull the bit in and go too deep)
  4. Drive in screw, using correct torque setting on drill driver (start on low torque setting, increase until correct)

So, if you own 4 cordless drills, then this will be quick and easy!! If you don't, quick change hex shank bits are well worth buying.

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