Determine The Proper Size Of A Pilot Hole For Any Screw
Over the years, I must have inserted hundreds of screws into wood, and one thing that has been constant is the importance of ensuring that the screws are inserted properly. It may sound simple, but the question of how large to make the pilot hole constantly arises.
The proper size of the pilot hole is the one that allows the screw threads to bite into the wood without the shank of the screw binding in the wood. Slight adjustments must be made to the pilot hole size when screwing into either softwoods or hardwoods.
Keep reading to find out everything you need to know about what size pilot hole should I drill, including the optimal size for any purpose and the debunking of some common myths.
Why Do I Need A Pilot Hole?
What do you think is the optimal size of the pilot hole for this screw?
In order to fully grasp the practicality of this, let’s first examine why drilling a pilot hole before screwing into wood is necessary.
The threads of a screw around the screw’s shank or body. The threads of the screw are what actually penetrate the wood and tighten it into the hole.
A pilot hole is drilled before a screw is used to remove any excess wood from the wood’s surface and allow the screw’s threads to make contact with the wood. If you don’t do this, the wood, especially hardwoods or MDF, may crack.
To avoid the lumber cracking as it ages, drill a pilot hole first.
Watch this short video to learn how to choose the correct pilot hole size.
Are You Screwing Into Softwood Or Hardwood?
Finding the best size pilot for the job at hand will be much easier once you’ve answered this question.
In most cases, a larger pilot hole is not necessary when working with softwoods, and vice versa is not suggested. Most plywoods can be screwed directly into the face without the requirement for a pilot hole. When screwing into the end grain, you should always drill a pilot hole first.
The pilot hole size for hardwoods, on the other hand, should be somewhat increased. After drilling a standard pilot hole, the screw threads still had trouble biting into the extremely hard wood I used for my last project. I went with the next-biggest drill size to get the job done.
Best Pilot Holes Sizes
The following tables of drill bit sizes include the pilot hole sizes I’ve found most useful throughout the years of using pilot holes. Where I’ve indicated a “little bradawl,” it’s because the hole is too tiny to accommodate the screw.
Each screw type has a suggested hole diameter. These tables might be useful to have on hand in the workshop; please feel free to print them out. Check out the paragraph that follows these tables for an alternative method of determining the appropriate size of pilot hole to use.
Drill Bit Size Chart
Imperial Chart
| Gauge | Inches | ||
| Screw Size | Clearance Hole | Pilot Hole (Softwood) |
Pilot Hole (Hardwood) |
| 0 | 1/16 | Small Bradawl | 1/32 |
| 1 | 5/64 | Small Bradawl | 1/32 |
| 2 | 3/32 | Small Bradawl | 3/64 |
| 3 | 7/64 | Small Bradawl | 1/16 |
| 4 | 7/64 | Small Bradawl | 1/16 |
| 5 | 1/8 | Small Bradawl | 5/64 |
| 6 | 9/64 | 1/16 | 5/64 |
| 7 | 5/32 | 1/16 | 3/32 |
| 8 | 11/64 | 5/64 | 3/32 |
| 9 | 3/16 | 5/64 | 7/64 |
| 10 | 3/16 | 3/32 | 7/64 |
| 11 | 13/64 | 3/32 | 1/8 |
| 12 | 7/32 | 7/64 | 1/8 |
| 14 | 1/4 | 7/64 | 9/64 |
| 16 | 17/64 | 9/64 | 5/32 |
| 18 | 19/64 | 9/64 | 3/16 |
| 20 | 21/64 | 11/64 | 13/64 |
| 24 | 3/8 | 3/16 | 7/32 |
Metric Chart
| Gauge | Millimeters (mm) | ||
| Screw Size | Clearance Hole | Pilot Hole (Softwood) |
Pilot Hole (Hardwood) |
| 0 | 1.6 | Small Bradawl | 0.8 |
| 1 | 2.0 | Small Bradawl | 0.8 |
| 2 | 2.4 | Small Bradawl | 1.2 |
| 3 | 2.8 | Small Bradawl | 1.6 |
| 4 | 2.8 | Small Bradawl | 1.6 |
| 5 | 3.2 | Small Bradawl | 2.0 |
| 6 | 3.6 | 1.6 | 2.0 |
| 7 | 4.0 | 1.6 | 2.4 |
| 8 | 4.5 | 2.0 | 2.4 |
| 9 | 5.0 | 2.0 | 2.8 |
| 10 | 5.0 | 2.4 | 2.8 |
| 11 | 5.5 | 2.4 | 3.2 |
| 12 | 5.5 | 2.8 | 3.2 |
| 14 | 6.5 | 2.8 | 3.6 |
| 16 | 7.0 | 3.6 | 4.0 |
| 18 | 7.5 | 3.6 | 5.0 |
| 20 | 8.5 | 4.5 | 5.5 |
| 24 | 9.0 | 5.0 | 5.5 |
How To Pick A Pilot Hole Drill Size On The Go
You’ll be able to grab a drill bit without always referring back to this table as you gain experience.
You can do this by placing the screw under the light and the drill bit in front of it. A proper drill bit can be identified by its ability to conceal the screw’s shank while revealing its threads.
Drive a screw in with this drill bit and see how it goes. As I indicated before, the hole size needs to be adjusted depending on the type of wood being used. Just a little bit of practise and you’ll be able to drill holes of the perfect size every time.
What Size Drill Bit Do You Use?
An appropriate size for a pilot hole is one that allows the shank or body of the screw to pass through while still allowing the threads to grip the wood fibres.
What Is The Difference Between A Pilot Hole And A Clearance Hole?
You may have noted that I included both pilot hole and clearance hole dimensions in the table above; but, what exactly is the distinction between these two?
Any time a screw is going into a second piece of wood, a pilot hole must be drilled first. As was previously established, it’s the dimension of the screw’s shank that allows the threads to penetrate the wood.
First, a clearance hole is bored into the first board. The diameter of the clearance hole should be only slightly bigger than the screw’s thread diameter. Read this article to learn more about the need of a clearance hole.
The red arrow in the following illustration indicates a clearing hole.
Cutout for screw clearance
What is a clearance hole and why do I need one?
The screw threads need to clear the timber otherwise they would bind and cause jacking. With the clearance hole, the two parts may be pulled together securely. I’ve written an article that goes into further detail.
Can I Screw Timber Without A Pilot Hole?
Without going into too much detail, yes, you can screw wood together without first drilling a pilot hole. Without first drilling a pilot hole, a screw will always go in the direction of least resistance when being driven into wood.
As a result, the screw may enter at an incline, and in extreme cases, it may even protrude through the surface. When putting a box together or screwing into end grain, this is almost always the case.
When a pilot hole is not drilled, the screwdriver tip frequently comes loose from the screw. Find out why here.
You can screw wood without first drilling a pilot hole, but that’s not a good idea. Your work will look more professional, and there will be less chance of wood splitting.
Does This Mean I Need 2 Holes For Every Screw?
Yes, I would recommend drilling 2 holes for every screw if you want your product to go together securely and neatly. You’ll be disappointed to hear this, but it won’t take long at all. BUT WAIT, there’s another option that won’t take as long as swapping the drills.
You should pick up some of these step drills, as shown below. I rely on them frequently.
Get some countersink pieces for your workshop.
Exercises in 5 Easy Steps
Exercises in a 5 Stage Format
I’ll demonstrate how to quickly and easily drill a pilot and clearance hole for your screws if you’d rather not invest in one of these step drills.
You’ll need two different drills to accomplish this. In the average workshop, you’ll find multiple drills. Not having one will make your life much more difficult, so I recommend getting another one. I rely on and advocate for the ones listed above.
Insert the smaller drill bit needed to create the clearance hole into one drill. Put your larger drill for the clearance hole into the second drill. After that, you can simply drill the pilot holes and clearance holes one after the other. It happens far more quickly than you’d expect.
The best part is that your finished product will look great.
How Do I Know If My Pilot Hole Is Too Big?
The screw should tighten as it is driven into the wood, biting into the material and eventually burying the screw head. When a screw is torn out of wood, it will spin in one place after reaching the head. This indicates that the pilot hole was oversized.
For this reason, you should always test your pilot hole on a scrap piece of material to ensure it is the right size before committing to the final hole. As I mentioned before, you’ll quickly learn with some practise if you’re using the right size drill.
Do I Need A Countersink Hole?
Using a countersink bit will result in a much cleaner and more precise finish. The screw head can then be concealed within the wood.
Hardwoods almost usually require a countersink, but softer woods may not. There are wood screws available with little protrusions beneath the screw head. These are what “chew” the wood, driving the screw head flush with the board’s surface.
A countersink bit may be necessary if the wood screws you are using have a flat underside to their heads. Just try one out on some scrap material first.
Drilling a hole that is both a pilot hole and a countersink at the same time is much simpler than drilling two separate holes. In the picture below, you can see the drills I keep in my workshop. They come in quite handy.
Conclusion – What Size Pilot Hole Should I Drill?
For the best results, use a pilot hole that’s the same diameter as the screw’s shank but narrower than the threads. When working with wood, a pilot hole is a must. The end product will be significantly better in terms of both joint strength and tidiness.
Also, the less time you spend trying to piece together the task at hand, the less stressed you’ll be. We should enjoy ourselves in the workshop as much as possible, as I always recommend.
A work well done is a job well done indeed.
