When you need to drill a pilot hole for a screw, you need to make sure you have the sizing correct. However, sizing is not quite straightforward, as you need narrower holes for soft materials than hard materials.
Drill Bit Sizes For Drilling Screw Pilot Holes
|Size of screw||Pilot hole for hardwood(inches)||Pilot hole for softwood(inches)|
Figuring Out What Size Drill Bit You Need For #8 Screw
The drill bit you use to make the pilot hole determines how large or small the diameter of the hole will be. You don’t want to use the same size drill bit as the screw, though, as you want to leave a little bit of material for the threads of the screw to catch on to.
There are many different drill bit sizes, and many sizes are standardized and can be found in most kits. ISO standard sets refer to sizes in millimeters, and the ANSI standard uses the imperial system and fractions of inches.
Also, commercial drill bits have a slightly smaller diameter than the number written on the bit. This is to allow for a little bit of movement during the drilling process which can widen the hole a little.
Figuring out what size drill bit for #8 screws will help you create pilot holes that allow for these fasteners to connect materials securely.
How Does Drill Bit Sizing Work for #8 Screws?
The easy way to think about the correct drill bit for #8 screws is to match the drill bit size to the diameter of the screw shaft itself(not accounting for the threads).
This allows the threads to catch the material and form a strong hold.
You can’t use this blindly and in every situation, though. Different materials behave differently, and in some cases, you may want the screw to penetrate more into the material.
Also, consider the bit you are using. Straight bits make straight holes with flatter bottoms, like a U shape. Tapered bits make holes with slightly slanted walls and a sharp bottom, like a V shape.
Tapered bits force the screw to push through even more of the material, allowing for a stronger joint. It’s more difficult to screw it in, but once it’s fastened, it will hold very strongly.
The #8 screw has a diameter similar to a 1/8″ straight drill bit.
For a tapered hole, use a slightly larger diameter like 11/64″.
What Is a #8 Screw?
There is a standardized screw sizing system that has 16 sizes and indicator numbers that go from 000 to 14. In the table above, we listed the sizes from 1 to 12 as they’re the most common.
#8 screws have a diameter of 0.164″ or nearly 5/32″. #8 screws have 40, 36, or 32 threads per inch of length.
#8 screws are very common fasteners and have a wide range of applications.
They’re an important part of every woodworker’s toolkit, since you can use them to attach wood to wood, attach a board to a door frame, attach boards to studs, and even to secure thick boards.
They’re also usable with sheet metal.
Do Different #8 Screws Need Special Drill Bits?
Not all #8 screws are the same! Depending on the type of #8 screw you have, you may need to change the drill bit you use:
- Use a straight bit for machine screws that have a flat point
- Use a straight or tapered bit for screws with a self drilling tip
The material will also make a difference in the pilot hole size.
Since it’s easier to screw into softwoods(think cedar, pine, or spruce), you can use a narrower hole. Hardwoods require slightly larger holes, since you won’t be able to get the screw in otherwise.
Use these sizes for straight bits:
- 7/64” for softwood
- 1/8” for hardwood
Use these sizes for tapered bits:
- 5/32” for softwood
- 11/64” for hardwood
Sheet metal fasteners need 0.137″ if holes are pierced, and 0.113 to 0.128″ holes for drilled or clean punched.
Drywall needs wall anchors.
As you can see, drill bit size is a crucial factor for #8 screws, and indeed all screws. The reason we focused on #8 screws in this post is because they’re standard and are used nearly everywhere.