What Size Drill Bit for a 3/8” Bolt?

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⅜” bolts are commonly used for machinery and construction projects. It can be used in two ways fully threaded and partially threaded which relates to sizing. If you want to know what size drill bit for a ⅜” bolt is, read further.

What Size Drill Bit for a 3/8” Bolt?

A ⅜” bolt needs a 5/16” size drill bit in diameter. The length can vary, however, most people would use 6 inches in length. This ⅜; bolt is used a lot in DIY projects and is preferred to be used with various types of metal. A bolt is also different from a screw so do take note of that.

Drill bit and various woodworking tools on the table

It’s also used to re-thread jammed carbon steel. Do take note that this is different from the ⅜” wedge anchor. The ⅜” bolt can come in different thread pitches with 16 and 24 threads per inch. They also require different drill bit sizes in length.

  • 16 threads require 5/16” in length for a drill bit
  • 24 threads require 21/64’ in length for a drill bit

Tips for Using Medium Drill Bits

Consider Using Stud Finder

A stud finder ensures you are not drilling into a water pipe or electric cables. Drilling through electric cables can create a huge accident, like electrocuting yourself.

So, it’s best to use a stud finder as a safety precaution. It’s also useful to avoid hitting water pipes which can cause leakage and flooding in your home. You should use a stud finder when drilling with hazardous materials near the drilling spot.

If you’re drilling into an unfamiliar surface, it’s best to use a stud finder to ensure you are drilling precisely and accurately. It’s better to be safe than sorry.

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.

Drill with an attached drill bit

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.

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.


⅜” bolt is used in a wide variety of projects. There are only two specific drill bit size for these bolts so you better make sure you’re using them. Otherwise, your project could get compromised. The end result may not last long because the bolts aren’t secured.