What Size Drill Bit for a #8 Screw

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In most situations, a #8 screw calls for a 1/8” straight drill bit. However, the ideal size of the drill bit can vary depending on the material you’re using, and you’ll need a narrower pilot hole when working with soft materials.

How to Figure Out What Size Drill Bit for #8 Screw

Figuring out what size drill bit for #8 screws will help you create pilot holes that allow for these fasteners to connect materials securely.

The drill bit size indicates the diameter of the bit you’re using to create pilot holes for fasteners. The drill bit size is an indication of the diameter of the pilot holes you can create, but the bit size diameter shouldn’t match the screw diameter exactly to allow the threads to penetrate the material.

Person deciding what size drill bit for a #8 screw

There is a wide range of drill bit sizes, with some standard sizes you’ll find in most tool kits. If you’re using the ISO standard, you’ll refer to drill bit sizes in millimeters, while the ANSI system uses fractions of inches.

Keep in mind that most commercial drill bits have a diameter that is actually slightly narrower than the number indicated since the trajectory of the drill bit can shift slightly and will typically result in a wider diameter.

In manual applications with a center punch and drill, there is a tolerance of .080 inches or 2 mm in most cases. This tolerance drops to .020 inches or .5 mm for applications that require more precision.

How Drill Bit Sizing Works for #8 Screws

A good rule of thumb is to have the diameter of the bit match the shaft of the screw without accounting for the protruding threads. This rule allows the threads to cut into the material and act as a reliable fastener with no play.

However, you shouldn’t apply this rule of thumb in every situation. Don’t forget to account for the way different materials behave and how much weight the screw will hold.

It’s also important to consider different types of bits. If you use a straight drill bit, you’ll create U-shaped pilot holes with straight walls.

If you opt for a tapered bit, you’ll drill V-shaped pilot holes. A tapered pilot hole allows the screw to get more contact with the material. It can be more difficult to insert the fastener, but you’ll end up with a more reliable connection that can bear more weight. Typically, you would use a slightly larger drill bit diameter for a tapered pilot hole.

The closest match you can get to the diameter of a #8 screw without the threads is a 1/8” straight drill bit. This number translates to 0.125” or 3.175 mm.

Cordless drill

If you need to create a tapered pilot hole, opt for a tapered bit with a slightly larger diameter. An 11/64,” 0.171,” or 4.36 mm bit is your best option.

What Does a #8 Screw Mean?

There are 16 standard sizes in the screw sizing system, with numbers ranging from 000 to 14. A #8 screw has a diameter of 0.164.” The nearest fraction is 5/32.” A #8 screw can have 32, 36, or 40 threads per inch.

These screws are common fasteners with a wide range of applications. It’s important to know what size drill bit for #8 screw since you’ll come across these fasteners when working on many different projects.

Keeping some #8 screws handy is essential when working on wood construction projects. You can use #8 screws to connect wood to wood, attach wood boards to wall studs, secure thicker boards, and attach fiberboard to a door frame.

It’s also a popular option for sheet metal fasteners. You’ll often find #8 screws with pan heads and threads that cover the entire length of the screw for this application.

Do Different #8 Screws Need Different Drill Bits?

The answer is yes. The first thing you should do is check the tip of your #8 screws and choose the right type of drill bit. If you’re using machine screws with a flat point, you’ll have to use a straight bit.

If you have #8 screws with a self-drilling tip, you can use a straight or tapered bit, but a tapered bit will result in a stronger connection.

The material is another important consideration. Because it’s easier to get screw threads through softwoods like pine, cedar, or spruce, you should work with a narrow pilot hole to get a secure connection.

Cordless drill and screws

Here are the best drill bit sizes to use with a straight bit:

  • 7/64” for softwood, or 2.77 mm
  • 1/8” for hardwood, or 3.17 mm

If you’re using a tapered bit, here are the recommended sizes:

  • 5/32” for softwood, or 3.96 mm
  • 11/64” for hardwood, or 4.36 mm

For sheet metal fasteners, you’ll need a 0.137” pilot hole if you’re working with pierced holes. If you’re using drilled holes or clean punched holes, your pilot hole diameter can range from 0.113 to 0.128.”

For drywall, you’ll need to use wall anchors. Your best bet is to match the size of your drill bit to the diameter of the wall anchor you’re using, but you can go over by 1/16,” as long as the fastener won’t bear a lot of weight.

What Size Drill Bit Do I Use for #8 Screw?

A 1/8” straight jobber drill bit will provide a reliable pilot hole for the 0.164” diameter of a #8 screw. It’s a suitable drill bit size for working with hardwoods like oak, maple, or walnut and materials with similar properties. With softer materials, you’ll need a narrower pilot hole for a more secure fit. 

Get Started With #8 Screws

Choosing the right drill bit size is crucial when working with #8 screws. These screws are among the standard sizes you’ll find on a wide range of projects, and you should make sure you have the right drill bits for these screws since you’ll more than likely use them.

We recommend using a 1/8” straight drill bit for most applications, but don’t forget to consider the properties of the material you’re using. You should also consider using a tapered drill bit if you need a reliable fastener that will bear more weight.

An expert at home repair, remodel, and DIY projects for nearly 40 years. His first experience came in completely restoring an antique home. Completely redone from the inside out, and restored to its original form, the home is a featured design by renowned Southern California Architect Cliff May, considered to be the father of the California Ranch Home. Now Dennis spends his time on fine woodworking projects and tool comparisons.