What Size Drill Bit for a 5/16-18 Tap?

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5/16- 18 taps require pilot holes before you install them. Hence, it’s important to know what size drill bit a 5/16- 18 tap should be. If you use the wrong size, it might lead to dents and splits on the material.

What Size Drill Bit for a 5/16-18 Tap?

A 5/16- 18 tap needs a size drill bit of 17/64 inches or 0.2570 inches in decimals. This also translates to using the letter F or G drill. Although the letter F is better suited for this tap. The 5/16- 18 taps are part of the Unified National Coarse, much like the 8-32 tap.

The 5/16- 18 taps are commonly used to make new threads or re-thread jammed or damaged threads, just like the ½-13 taps with a drill bit of 27/64″. These taps are mostly used for metals and plastics. It is usually made out of high-speed steel for durability and efficiency.

Tips for Using Medium Drill Bits

Know Your Drill Speed

For medium drill bits, it’s important to know the speed of the drill. Drill bits get hotter the faster it spins. When drilling metal or bricks, most people would set their drills to low speed and pressure. This is to avoid overheating and damage to the drill.

The drill’s speed should be adequate for the size of the drill bits, which is medium. The bigger your drill bits are, the slower the speed should be. For medium drill bits, moderate speed is generally what you want. It helps you drill through metal and bricks faster and with better precision.

Maintaining the right speed helps prevent the drill from overheating. If you see smoke coming from your drill, it’s a sign that you should stop what you’re doing and let your drill cool down.

Use a Test Board

When drilling wood or metal, your medium drill bits can create a splintered hole on one side. This is called a blowout which most amateur DIY workers get often. Blowouts can damage your workpiece affecting its quality.

It can sometimes lead to accidents since the drill bursting through the hole will make you lose control when you’re careless.

To stop this from happening, you can use a test or spare board as a cushion to clamp the piece down. The spare board prevents any blowouts since it acts as a cushion when drilling a hole.

Deburr the Hole

Most medium drill bits are used for drilling holes. So, deburring the hole is a sensible thing to do. After you’re done drilling, make sure the hole does not have sharp edges or burr left in the hole. Feel the hole until it’s smooth.

It ensures your hole is smooth and clean, so you produce quality work. You can deburr a hole by running it in a bit of power and running the bit around the edges of the hole.

You can also use deburring tools to make the process simpler and easier. Most of them come with an instructional, so you should have no problems learning to properly use them.


5/16- 18 taps can be flexible regarding drill bit size, with the letter F or G drill being usable. However, it is recommended to use an F dri+ll for better results. These taps are commonly used for re-threading, so you should remember the drill bit size for this.