What Size Drill Bit For a 10-24 Tap?

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The term 10-24 tap can be confusing and make you wonder what size drill bit for 10-24 tap. You might feel confused about the size of the tap you are working with, as there are two numbers involved. You just need to get a few formulae on hand, and you are sorted to drill.

What Size Drill Bit For a 10-24 Tap?

The correct size drill bit for 10-24 tap is a #25 drill bit, the measurement being 5/32”.

A 10-24 cap comes in two different thread counts. Thus the size of the drill bit for each one is entirely different. In the world of so many other tapping, it is difficult to memorize what size of the drill bit you are supposed to use for each one.

In this article, you will understand the mathematics behind the process, and you will be up and going to work with any tap size.

Hand holding different drill bit sizes

Figuring Out The Drill Bit Size For 10-24 Tap

Figuring out the drill bit size for 10-24 tap begins with understanding the sizing differences of the tap. 

  • 10 and 24 in 10-24 are two different sizes that you need to work with. Thus you will need separate drill bits to work with different sizes.
  • To figure out the size of the tap, you have to start by looking at the specific length or the thread pitch.

After examining the dimensions, it is easy to figure out what size will sit well with your tap size.

Tap Sizing For 10-24 Tap

The tap sizing for 10-24 taps requires the examination of certain parameters and dimensions. This is how you can proceed further with the process:

  • The sizing will require an accurate count on the diameter of the tap, the desired percentage of the thread, pitch, and the size of the final hole.
  • The percentage of the thread does not matter on the size of the tap you have; it depends on the outcome.
  • Usually, the thread percentage lies between 75% to 85%, but the amount recommended by the professionals is 80%.

After finalizing the measurements you are going to work with, you can calculate the size of the drill bit you are going to use.

Calculating The Size Of The Tap Drill

For calculating the size of the tap drill, you need to be familiar with basic mathematics and the tap size you are working with.

  • Measure the diameter of the tap or read the number mentioned in the specifications of the tap.
  • Now, insert the diameter’s value into a simple mathematical formula, i.e., DH=DMB-.0130 (% of desired full thread/ Ni), here DMB is the diameter, and Ni is the other part of the tap.
  • Now insert the values for the tap size 10-24 and calculate for DH.
  • You will see that the answer sits well in the drill bit size named #25.

With the formula mentioned above, you can calculate the drill bit size for any tap size; just make sure the thread count is between 75% to 85%. Here is the link to the video guide to calculate the drill bit size for any tap size.

Why Different Sizes Are Needed For 10″ and 24″?

You might end up wondering why different sizes are needed for 10 and 24 tappings. You need to decode the difference in both for better understanding.

  • Both the taps might have the same diameter, but the thread pitch for each is different. Thread pitch is defined as the number of threads per inch.
  • The thread pitch has a considerable influence on the length of the tap. In the case of a 10″ one, the threads per inch will be comparatively less than the 24″ tapping resulting in different drill bit sizes. 
  • In the formula, the thread pitch is one of the main components. Thus it is quite clear the size of the drill bit will change for each dimension.
  • If you avoid calculating the size of the drill bit, you will end up with the wrong dimensions of the hole.

The wrong dimensions of the hole will not only stop the machine from functioning correctly but stop it from working at all.

Drilling With 10-24 Tap

Since all the calculations are brought into place, it is high time that you start drilling with 10-24 taps.

Drill bit set
  • Get all the dimensions in hand and choose the right drill size.
  • Make sure you place the material into the clamps to avoid any sudden slips or rotating.
  • Stick masking tapes on the material to provide ample space to mark the point where you want to drill the hole.
  • Put your drill at an angle of 90 degrees, make sure it is perpendicular to the metal. Even the slightest dip in the angle can make you end up with a crooked hole.

Do not forget to test the drilling process on a piece of scrap. It not only prevents any sudden accidents but also provides you confidence before making the final drill.

Frequently Asked Questions

Why Is It Necessary To Drill A Pilot Hole?

It is necessary to drill a pilot hole to decrease the chances of splitting the material into two parts. When we drill a pilot hole, the wedging is comparatively less when the screw is driven into the hole. The materials like plastic, wood, and concrete demand a pilot hole as these are not that hard materials to work with.

Why Most Of the Drill Bits Are Kept At An Angle of 118-Degrees?

The drill bits are usually kept at an angle of 118 degrees when you are working with softer materials like wood. The angle makes the drill steeper and more pointed. In addition, it results in the reduction of chisel, though for harder materials, this angle is not recommended.


The process of calculating and drilling might seem a bit overwhelming, especially when you are new and do not have a hand at tools. However, everything will fall in place once the calculations are done right; thus, make sure you take your time while making all the calculations.

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.