5/16-18 Tap Drill Size

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The precision in affixing screws often demands the crafting of a pilot hole prior to installation. When working with specific sizes like the 5/16-18 screw, it’s vital to pair it with its corresponding 5/16-18 tap drill size to guarantee a snug fit.

In the sections that follow, I’ve laid out comprehensive tables showing the screw dimensions, their paired hole diameters, and the ideal drill sizes to assist you in your tasks and projects.

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

From my experience, screws can often split wood or dent metals if the pilot hole isn’t just right or if one isn’t drilled at all. Beginning with the right pilot hole is always a wise move to save materials and ensure a smooth job.

5/16-18 Tap

It’s essential to choose the correct tap drill size at this stage. Refer to the table below to match the hole you need with the right drill bit size.

Screw Size: Threads Per Inch (TPI)Recommended Hole DiameterDrill Bit Size

Below is another table for drill bit sizes with 50% and 75% threads. It also includes the screw size, major diameter, and the threads per inch.

Screw Size

Major DiameterThreads Per Inch75% Thread50% Thread
(TPI)Drill SizeDecimal (in)Drill SizeDecimal (in)

What to Consider Before Drilling a 5/16-18 Tap

Drilling can save your tools and your wallet from wasted materials. If you consider drilling a pilot hole on your workpiece before installing the screws, here are the things you should keep in mind.

Drilling Process

Whatever drill bit size you’re going for, whether a 5/16″ tap or 1/4″ 20 tap, the drilling process [1] is the most crucial part of your project. If you do this step correctly, then the rest of the procedures that you have to follow will be easy and correct. Using the 5-16-18 tap, you must carefully drill a hole in the metal, plastic, or wood.

Make sure you apply enough force and speed to assist the tap in making the pilot hole. Start slowly to prevent breaking or damaging the top part of your workpiece. 

drill bits

Once you are almost in the middle, you may now speed up. Lastly, if you can feel the bottom, you must slow down again to prevent chipping the other side of your workpiece.

When I’m drilling, I make sure to keep the drill straight and ensure the tap is properly attached. This helps prevent any misaligned or oversized holes. A slanted drill can often lead to a hole that’s off or larger than intended.

Moreover, if the tap is not properly secured, it can fly away once you turn on the drill and cause damage to objects around it and even to you.

How to Use 5/16-18 Taps

5/16-18 taps are used to make new threads or re-thread jammed and/or damaged threads. You can use these taps for metals and plastics. It is usually made of high-speed steel, which makes it durable and efficient.

drill size for a 516-18 Tap

There are three main types of 5/16-18 taps: taper, plug, or bottom. Each has its distinct function. The taper style is usually used to start the thread square on the workpiece. 

The plug style is used to go through the hole. The bottom style creates threads to the bottom of the hole. You can buy all these three in a set.

These taps are very easy to use. They are also versatile and effective in creating the threads you need for your project. 


Pecking is a vital process whether you are tapping or drilling. It prevents bits from breaking or overheating. This technique involves drilling halfway through a part, then retracting the bit to remove the chips, allowing it to cool down.

applying oil on the surface of the tap

Whenever I remove the chips, I make it a habit to apply oil between the tap or drill and the workpiece. Typically, I rotate the handle for a full turn and then backtrack by half a turn, a method widely adopted by many in the field.


Selecting the correct 5/16-18 tap drill size is pivotal for precision in your work. Being well-informed about the right drill bit size not only conserves resources but also ensures cost-efficiency. 

Refer to the provided tap drill size tables above, taking special note of the 75% and 50% thread recommendations, to guide you towards optimal results.

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Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.

Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.

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