Most types of screws require to have a pilot hole before installation. If you are going to use a 5/16-18 screw size, then you also have to use the right 5/16-18 tap drill size to ensure that the screw will fit well.
Here are the tables that contain the screw size, correct hole diameter, and drill size for your reference.
What is the Drill Size for a 5/16-18 Tap?
Some screws can split up wood or dent metals if the pilot hole size is incorrect or if there’s no pilot hole. Drilling can be a good way to start any screwing job to prevent wasting materials.
Using the right tap drill size is very crucial in this stage. Look at the table below to ensure that you can make the right size of the hole using the correct drill bit size.
| Screw Size: Threads Per Inch (TPI) | Recommended Hole Diameter | Drill Bit Size |
| 5/16-18 | 0.2570″ | F |
| 5/16-24 | 0.2720″ | Ltr.l |
| 5/16-32 | 0.281 | 9/32 |
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 Diameter | Threads Per Inch | 75% Thread | 50% Thread | ||
| (TPI) | Drill Size | Decimal (in) | Drill Size | Decimal (in) | ||
| 5/16 | 0.313 | 18 | F | 0.257 | J | 0.277 |
| 24 | I | 0.272 | 9/32 | 0.281 | ||
| 32 | 9/32 | 0.281 | L | 0.29 | ||
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.
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.
We also suggest keeping the drill straight and the tap attached properly to avoid making a wrong hole. A slant drill can cause a slant or bigger hole.
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.
5/16-18 taps are available in taper, plug, or bottom. Each one of them has its own function and advantages. 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
Whether you are tapping or drilling, pecking is an important process. Pecking ensures that the bits won’t break or overheat. It is a process of drilling halfway through a part, then retracting it to remove the chips allowing it to cool.
You can apply oil on the surface between the tap or drill and the workpiece whenever the chips are removed. The common practice the workers do is to rotate the handle for a full turn and then back a half turn.
Conclusion
Using the right 5/16-18 tap drill size can make your job more accurate. Moreover, if you know which size of drill bit you need to use, it will save you money and other resources in the long run.
Use the tap drill size tables above as your references for the proper sizing, including the 75% and 50% threads.
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