FASTENER BUYING MADE SIMPLE:
IDENTIFYING THE RIGHT UTS SCREW FOR YOUR APPLICATION
This guide will help you understand the variety of Unified Thread Standard (UTS) screws that we carry, along with their functions. UTS screw threads are also commonly called “machine screw threads” or “cap screw threads”. The guide also contains information on the naming structure used for these screw styles to help you navigate the complex nomenclature used in their product descriptions.
WHAT IS UNIFIED THREAD STANDARD (UTS)?
Unified Thread Standard (UTS) is the established standard for matching / mating fastener threads in the US and Canada, ensuring compatibility and consistency across applications. It is primarily used for certain types of screws, nuts, and bolts, providing diameter size and thread count guidelines to guarantee that these parts will work together properly.
UTS makes a further distinction between coarse threads – Unified National Coarse (UNC), and fine threads - Unified National Fine (UNF). Depending upon the job, you will need to consistently use one or the other for matching sets of threads.
See Unified Thread Standard chart for common UNC and UNF sizes (diameter / thread count).
| Screw Size | UNF | UNC |
|---|---|---|
| #0 | 0-80 | |
| #1 | 1-72 | 1-64 |
| #2 | 2-64 | 2-56 |
| #3 | 3-56 | 3-48 |
| #4 | 4-48 | 4-40 |
| #5 | 5-44 | 5-40 |
| #6 | 6-40 | 6-32 |
| #8 | 8-36 | 8-32 |
| #10 | 10-32 | 10-24 |
| #12 | 12-24 | |
| 1/4" | 1/4-28 | 1/4-20 |
| 5/16" | 5/16-24 | 5/16-18 |
| 3/8" | 3/8-24 | 3/8-16 |
| 7/16" | 7/16-20 | 7/16-14 |
| 1/2" | 1/2-20 | 1/2-13 |
SCREWS IN UNIFIED THREAD STANDARD (UTS)
These are among the most common types of fasteners. They are externally threaded fasteners featuring heads in a variety of shapes and styles along with varied mechanisms for driving / installing them. They are used with matching nuts or a pre-tapped matching threaded hole to make a fastening connection and provide superior strength than other screw thread styles.
MACHINE SCREWS
Machine Screws are the most common fasteners used for a matching connection to a nut or threaded hole, especially in sizes under ½”. They consist of an externally, fully threaded body with a head on one end and a flat, blunt tip on the other. Sizes range from 0-80 up to ½-13 and ½-20. Machine screws are available in a wide variety of head and drive styles allowing for different needs based on clearance space required, appearance, and preferred driving / installation method. Stainless steel options are available, with steel parts offered in many finish and color variants.
Example of a Machine Screw Description:
On this part, the “4-40” indicates the diameter size and the thread count. It is a size 4 diameter with 40 threads per inch. The 1” indicates its length. It is driven by a phillips bit, has a pan shaped head, and is made out of steel with a zinc finish.
SEMS SCREWS
SEMS screws are machine screws with lockwashers pre-attached under the head in order to provide a stronger hold or decorative appearance. Variables will include head and drive styles as well as options for different styles or combinations of pre-attached washers. Stainless steel options are available, with steel parts offered in many finish and color variants.
Example of a SEMS Screw Description:
On this part, the “6-32” indicates the diameter size and the thread count. It is a size 6 diameter with 32 threads per inch. The 5/16” indicates its length. This part features a square cone style washer. It is driven by a torx driver / bit, has a pan shaped head, and is made out of steel with a zinc finish.