Pilot Holes: Why to Use the Right Drill Bit and Countersink

Do you really need to drill a pilot hole before screwing two boards together?

Yes!!

See why and which bit size to use so you have strong wood joints.

And see tips on using countersinks for flush and recessed screw mounts.

You’ll be driving screws like a pro!

Why Pilot Holes Are a Must

• The #1 reason to drill a pilot hole is to keep your wood from splitting.
• The #2 reason is to have a cleaner, tighter fit for the screw.

After you drill a hole, you must have noticed all of the sawdust that comes out when you pull the bit out.

The same churn of wood happens when you put in a screw without a pilot hole.

But, you’re asking the screw to chew through all that and keep going deeper into the wood.

A pilot hole clears the path for the screw so that it can get a solid grip and hold tight.

Are Countersinks a Must?

Well, that depends.

Countersinks allow:

• the screw head to be flush with the material.
• or, the screw head to be recessed so you can use wood filler or a plug to cover.

For soft woods, like pine, a countersink may not be needed, as you can usually just drill a wee bit longer to get the head flush.

But for hardwoods, countersinks are a must if you want the screw head flush, or to hide it completely below the surface by placing wood filler or a plug above it.

An all-in-one bit/countersink is the easiest, and most accurate type to use.

There are all kinds, and we’ll discuss those in a moment.

But let’s talk about the bits first.

What’s the Right Size Drill Bit to Use?

Which drill bit you use for the pilot hole depends on 4 factors:

• Type of wood
• Size of screw
• Type of screw thread
• Type of screw head

Pilot Hole Bit Size Rule of Thumb

Soft wood – like pine

• Drill a pilot hole that is a little smaller than the screw.
• Use a course threaded screw as it needs more wood to bite into, hence the smaller pilot hole.

Hard wood -like oak

• Drill a pilot hole the same size as the screw.
• Use a fine threaded screw for hard woods as it can’t chew through the wood as easily or deeply as a course threaded screw. So the hole needs to be clean and as close to the screw size as possible.

Match Drill Bit to Screw Size

If you’re building with pine, nothing beats a good #9 construction screw for a secure hold.

So, that’s why I used it in this example.

The screw is 11/64” in diameter.

The rule of thumb is to go down 1/64: in size with the drill bit.

Yeah, I know you don’t want to do the math, so I’ve done it for you.

• That would be a 5/32” bit.
• You can also use a 9/64” or even a 1/8” bit will do just fine.

A #8 screw is 5/32”.

• Use a 9/64: or even a 1/8” bit for it.

A #10 screw is 3/16”.

• Use 11/64” or 5/32” with it. Or, a 1/8” bit.

Seeing a pattern here?

For DIY shop projects I generally use a 1/8” bit for all pine woodwork.

For hardwoods, no math is needed. Use the same size bit as the screw.

And maybe rub a little bar soap on the screw to make it glide in (although some woodworkers claim this introduces moisture that can rust the screw).

What if I Don’t Know the Screw Size?

Yep, I’ve got a few butter tubs filled with odd and end screws too.

Guess what? You don’t have to know the size!

Here’s the quick and dirty way to do it:

• Just hold the bit over the screw, as shown below.
• Point the bit end toward the head of the screw.
• You have the right bit when it covers the screw body, but some screw spirals are still showing.

Countersink Bits

To get those screws nice and flush, or even below the wood surface so you can fill them in, you’ll want to use a countersink bit.

Basic countersink types:

• Fixed – the bit cannot be changed or moved
• Collard – the bit can be replaced when worn, or moved up and down to match the screw length
• Tapered – the tip of the countersink is V shaped. The bottom of the screw head should also be V shaped. This is the most common type of countersink.
• Flat – the tip of the countersink is flat. The bottom of the screw head should also be flat.

Since my #9 construction screw heads are V shaped, I use a tapered countersink.

I also like the convenience of a collar so I can change the bit when worn. I have yet to need to move the depth, as I’m always using it for longer screws.

Countersink Depth

For most folks, including me, it comes down to eyeballing while drilling.

For the screw head to be flush, you don’t have to go very far down when using a tapered bit.

For a recessed screw head, just drill the countersink a little deeper.

And, if you’re using an impact driver on soft wood like pine, it’s likely going to drive the screw much further down, past the countersink anyway.

TIP: I would use a drill with a torque adjustment instead of an impact driver if you want to ensure flush mount on the screw head.

How Do You Do It?

Do you use pilot holes?

How about countersinks?

Leave us a comment with your tips.

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