Threaded Holes: Types, Methods, and Essential Guidelines

treaded holes

Have you ever wondered how components in machines and devices stay securely fastened together, resisting vibrations and loads? Threaded holes are a cornerstone of mechanical assembly, allowing screws and bolts to be tightly and accurately inserted.

Whether it’s the finesse needed for a blind hole or the precision required for threading deep cavities, machining threaded holes demands expertise.

In this blog post, we will unravel the mysteries of threaded holes in CNC machining, exploring the various types, the methods employed to create them, and the essential guidelines that ensure success. Prepare to delve deep into threaded holes? We promise you’ll emerge with valuable insights and the knowledge to apply them effectively in your next project.

Types of Threaded Holes

Understanding the nuances between different types of threaded holes is fundamental for engineers and machinists alike. The two primary categories we encounter are Blind Threaded Holes and Through Threaded Holes, each with its own set of characteristics and applications.

blind hole and through hole

Blind Threaded Hole

A blind threaded hole does not go all the way through the material. This type of hole ends inside the component, creating a bottom. It’s essential for applications where a secure endpoint is needed without piercing through the entire material. Blind holes are critical in maintaining the integrity of sealed enclosures or when the other side of the part cannot have a visible opening. Precision in drilling depth and threading is crucial to ensure the functionality and strength of the assembled parts.

Through Threaded Hole

Conversely, a through threaded hole passes completely through the material, allowing a bolt or screw to extend out the opposite side. This type is advantageous for applications requiring bolts to be secured with a nut or when the assembly needs to be fastened to another component. Through holes facilitate easier alignment and can accommodate slight variations in the length of the fastening hardware. Their straightforward nature, however, requires careful consideration of the material’s thickness to ensure adequate thread engagement and load distribution.

Both types of threaded holes play pivotal roles in mechanical design and assembly, making the choice between them dependent on the specific requirements of the project at hand. Understanding their distinctions enables machinists to make informed decisions, ensuring the durability and reliability of the final product.

Making Threaded Holes: A Step-by-Step Guide

Making threaded holes with precision is essential for the integrity of any mechanical assembly. Here’s a streamlined guide to creating the threaded hole:

Preparing and Drilling the Hole:

Selection of Material: Choose the appropriate material, considering the intended use and environmental factors.

Drill the Initial Hole: Use a drill bit that matches the inner diameter of your intended thread. Ensure the hole depth accommodates the thread length, adding extra depth for blind holes.


Creating a Lead-In: After drilling, chamfer the top of the hole. This beveled edge aids in aligning the tap and reduces the risk of thread damage during the tapping process.

Tool Selection: Use a chamfer tool or a larger drill bit at a shallow angle to create a smooth transition into the hole.

Tapping the Hole:

Choosing the Tap: Select a tap that matches your thread specifications. Remember, the tap size and thread type should align with your project’s requirements.

Applying Lubricant: Before tapping, apply a suitable lubricant to both the tap and the hole to minimize friction and wear.

Tapping Process: Insert the tap into the hole and turn it clockwise to start cutting the threads. After a few turns, reverse slightly to break any chips that may form. Continue until the tap passes through the entire depth of the hole.


Manual or Automated Tapping:

Manual Tapping: Best for low-volume or highly precise applications. It allows for careful control but is slower and more labor-intensive.

Automated Tapping: Ideal for high-volume production. Machines can tap holes quickly and consistently. Requires setup and programming but significantly increases efficiency.

Whether tapping by hand or using a machine, maintaining alignment and applying consistent pressure are keys to creating high-quality threads. Following this guide ensures a fundamental understanding and application of techniques essential for anyone involved in CNC machining or mechanical design.

Threaded Holes Design Considerations

In designing threaded holes for CNC machining projects, several key factors must be carefully considered to ensure the effectiveness and durability of the final product:

Thread Types and Sizes: The selection between types such as UNC (Unified Coarse), UNF (Unified Fine), or metric measurements impacts both the application’s compatibility and performance. Each thread type serves distinct purposes, from general fastening to precision applications.

Depth of Thread: Adequate tread depth is critical for the fastener’s holding power. A common guideline is that the thread engagement should be at least 1.5 times the diameter of the fastener. The internal thread in a threaded hole can be either cut using a cutting tool (a cutting tap or single lip cutting tool) or formed using a forming tap.

Material Selection and Hardness: The material’s properties significantly influence the thread’s quality and the hole’s durability. Harder materials may offer more strength but require specific tools and techniques to effectively thread.

Nominal Sizes and Custom Threads: While nominal sizes offer ease of use and compatibility, certain projects may necessitate custom threads for unique applications. However, creating custom threads can be more complex and costly, necessitating careful consideration.

What Are the Differences Between Tapped Holes and Threaded Holes?

Threaded holes and tapped holes are often mentioned in CNC machining and assembly processes, yet they carry distinct characteristics:

Process: Threaded holes are typically pre-made during manufacturing, whereas tapped holes are created by cutting threads into pre-drilled holes.

Speed: Tapping holes can be slower due to the manual or machining process required to cut threads. In contrast, threaded holes, being pre-made, eliminate this step, offering quicker assembly readiness.

Flexibility: Tapped holes allow for more flexibility in terms of location and depth, as they can be added as needed to a component. Threaded holes, being predetermined, lack this adaptability.

Material: While both methods can be applied across a range of materials, the choice of tapping or using pre-threaded holes may depend on the material’s hardness and the application’s requirements for strength and durability.

Cost: Initially, tapping holes may seem more cost-effective, especially for custom or unique applications. However, for high-volume production, the cost of creating threaded holes can be lower due to the efficiency of mass manufacturing processes.

Each method has its place, depending on the specific requirements of the project, including the need for customization, production volume, and material characteristics.


This blog delved into the essential types, methods, and considerations for creating durable and precise threaded connections. From understanding the distinction between blind and through threaded holes to mastering the steps Threaded Holes: Types, Methods, and Essential Guidelines of drilling, chamfering, and tapping, we’ve covered the foundational knowledge necessary for anyone looking to strengthen their CNC machining projects.

If you’re ready to take your projects to the next level with professional-grade threaded holes, look no further than CNCfirst. Our expertise in CNC machining allows us to deliver high-quality prototypes and parts tailored to your specific needs. Contact us today to start your project.


How do you determine the correct size for a threaded hole?

The size of a threaded hole depends on the bolt or screw it’s meant to accommodate. First, identify the hole diameter and thread pitch of the fastener. Then, consult a tap drill chart, which matches tap sizes to drill bit diameters for pre-drilling holes before tapping. This ensures compatibility between the threaded hole and the fastener.

Can you repair damaged threads in a threaded hole?

Yes, damaged threads in a threaded hole can often be repaired. Techniques include using a thread repair kit, which typically involves drilling out the old threads, tapping the hole to a larger size, and inserting a helicoil or thread insert that matches the original thread size. This restores the threaded hole’s functionality.

What materials are suitable for threaded holes?

Materials suitable for threaded holes include metals like aluminum, steel, and brass, which offer durability and resistance to stripping. Plastics and composite materials can also be threaded but may require special considerations for thread depth and load-bearing capacity to avoid damage.

How does thread pitch affect the strength of a threaded connection?

Thread pitch, the distance between thread peaks, significantly impacts a connection’s strength. Finer pitches, with more threads per unit length, often provide greater strength due to a larger contact area and better load distribution. However, they require more precise alignment and are more susceptible to damage from over-tightening.