It’s probably due to threads being cut or cast using tooling for the actual shank diameter, where slightly too much material is removed either intentionally or due to manufacturing tolerances.

Why do screws have different threads?

Each one is tailored to different tasks and different material sizes. Some will require pre-drilled holes while others have sharp designs meant for drilling directly into softer materials like wood. Other screws vary in thread spacing, which is important for various characteristics of the screw.

What is nominal diameter of screw thread?

The size most commonly associated with screw threads is the nominal diameter. Nominal diameter is a more of a label than a size. For example, a bolt and nut may be described as being ½” diameter.

What is the diameter of a screw based on?

Diameters of Screws / Bolts

To measure the diameter of screws and bolts, you measure the distance from the outer thread on one side to the outer thread on the other side. This is called the major diameter and will usually be the proper size of the bolt.

What is the difference between UNC and NC threads?

Coarse threads have a larger pitch ( fewer threads per inch, or a bigger distance between the threads) compared to fine threads.

NC ( National Coarse )
Size ( Diameter ) Threads per Inch
1/4″ 20
5/16″ 18
3/8″ 16

What does thread size mean for screws?

Inch thread sizes are specified by diameter and threads per inch. Diameter is also known as screw size. For those with a diameter smaller than 1/4″, screw size is indicated by a number (e.g., #10 or No. 10). For example, a 10-24 screw has 0.190″ thread diameter and has 23 threads per inch.

What are the different screw thread sizes?

There are three standard thread series in the Unified screw thread system that are highly important for fasteners: UNC (coarse), UNF (fine), and 8-UN (8 thread).

Are UNC and NPT threads compatible?

Most North American hydraulic and pneumatic components are compatible with National Pipe Threads (NPT), or Unified Threads (UN/UNF).

Is NPT and NC the same?

UNC is Unified Coarse thread , the successor to the obsolete National Coarse (NC) thread. UNF is Unified Fine thread, the successor to the obsolete National Fine (NF) thread. NPT National pipe thread is used (in the U.S.) for plumbing of water and gas pipes, and threaded electrical conduit.

Which is stronger UNC or UNF?

A 1/4 UNF thread is about 14% stronger than its UNC counterpart. Coarse threads are slightly stronger (against stripping) per length of engagement than finer threads (see thread strength section below).

Are UNC and UNF interchangeable?

An Overview of The Unified Screw Thread Series

This standard helps to make sure that screws, bolts and other threaded fasteners are compatible. They’ll work with each other regardless of manufacturer or country. UNC and UNF are both symbols in the Unified Screw Thread Standard.

Are UN and UNC threads the same?

UNF and UNC are two symbols of Unified Screw Thread Series, which defined based on the amount of threads per inch and standardized with gauge. UNF threads are Unified fine pitch threads, while UNC threads are Unified coarse pitch threads.

Is coarse or fine thread stronger?

fine thread

For fasteners with the same nominal size, fine thread fasteners are stronger than coarse.

What are advantages of coarse threads over fine threads?

Coarse threads are more durable and have greater resistance to stripping and cross-threading. The height of each thread is greater than the corresponding fine thread so there is more material between each thread making flank engagement greater.

What is the difference between right hand and left hand thread?

Screw Handedness: Left-Hand Thread and Right-Hand Thread

Screw handedness refers to the direction that a screw’s thread wraps around its shaft. Right-handed threads run clockwise, and left-handed threads run counterclockwise.

What are the advantages of coarse threads?

Coarse threads tap better into brittle materials and are less likely to cross thread. Coarse threading lends itself to thicker coatings and platings before thread adjustments need to be made.

When should screws with coarse threads be used?

Coarse threads are used when threaded into aluminum or cast iron because the finer threads tend to strip more easily in these materials. Are stronger when assembled with lower strength nut or tapped hole materials. Stronger for bolt/screw/nut sizes over one inch.

What causes thread galling?

Galling occurs when threads are damaged by material sticking and getting torn off. Galling is a common type of damage that can occur in threads. When galling happens, it appears as though chunks of thread have been torn out and torn lumps of the removed material may be visible.