Machine Screw Diameters Chart and Unified National Thread Sizes – What is a Machine Screw | CNCLATHING


Machine screws are designed to join parts together through threaded holes. The small size and unique threading design of machine screws make it different from other types of screws and have an advantage in lots of applications. Here we’ll talk about what is a machine screw and how does the thread work, check out the US Machine Screw Diameter Chart and Unified National Thread Sizes at our site if you are in need.

What is a Machine Screw?

A machine screw is a unique type of fastener that defined as featuring a diameter of up to 0.75 inches by The American Society of Mechanical Engineers (ASME). In addition to the machine screw size, it’s also characterized by its uniform threading from the top to the bottom, which means that the entire length of the threaded section of the screw retain exact same diameter, while the thread can come in coarse or fine type, like UNC thread and UNF thread. Machine screws are designed to be threaded into uniformly threaded nuts or holes that existed in the parts that are intended to fasten, commonly used in electronics, tools, appliances, and machinery applications. Even though with distinctive features, machine screws also can be fabricated in various materials, driver head types, sizes, diameters and configurations.

What’s the Difference Between Machine Screw and Bolt?

Bolts and machine screws have no much difference on their construction and shapes, they generally differ in uses. All machine screws can be used as bolts but not all bolts can be machine screws. 

1. Machine screw sizes are generally considered to be smaller than bolts

2. Machine screws are typically used in threaded holes or threaded parts to secure of fasten two parts together, while bolts are usually used with nuts and washers with a clearance hole to join them together.

3. Machine screws can be designated as bolts if the primary tightening of the fastened joint is accomplished by turning the head of the screw. 

4. Generally speaking, if it’s got screw threads and hex head, it’s a bolt. If it’s got a slotted head, either Phillips or Flat, it’s a screw. 

Types of Machine Screws

There are two common machine screw types with coarse threads or fine threads. Coarsely threaded screws are stronger than fine threads and can screw in more quickly, as they have fewer threads on the same length and the threads are higher, best for thick materials and coatings. Finely threaded screws are better than coarse ones in tension and shear, they are better for harder and thinner materials, or precise products. The Unified Screw Thread System and ISO Metric Screw Thread System are two major systems to classify the machine screws, based on inches and millimeters, separately. Machine screw sizes chart for the most common UNF (Unified Fine) and UNC (Unified Coarse) in The Unified Screw Thread System are provided at CNCLATHING.COM. As a professional CNC machining services supplier, we can produce custom screws and other fasteners for your specific applications.

US Machine Screw Diameters Chart

Here is a table featuring diameters of US machine screws, the complete Unified National Thread Sizes chart please check our guide. The thread diameter is measured on the outside of the threads.