A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is an inclined plane wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. More screw threads are produced each year than any other machine element.[1]
Threads are generally produced according to one of the many standards of thread systems. Standards Development Organizations such as the American National Standards Institute, American Society of Mechanical Engineers, SAE International, International Organization for Standardization, Deutsches Institut für Normung (German Institute for Standardization), British Association and others produce these standards for manufacturers to follow when producing threaded components.
| Standard | Name | Type | Example |
|---|---|---|---|
| ASME B1.1-2003 (R2018) | Unified Inch Screw Threads (UN and UNR Thread Form) | V Thread Form | 1⁄4″-20 UNC #4-40 UNC |
| ASME B1.5-1997 (R2014) | Acme Screw Threads | Trapezoidal Thread Form | Tr 60×9 |
| ANSI/ASME B1.9-1973 (R2017) | Buttress Inch Screw Threads | Breech-Lock Thread Form | |
| ASME B1.10M-2004 (R2014) | Unified Miniature Screw Threads | V Thread Form | 0.60 UNM |
| ANSI/ASME B1.11-1958 (R2016) | Microscope Objective Thread | V Thread Form | |
| ASME B1.13M-2005 (R2015) | Metric Screw Threads: M Profile | V Thread Form | |
| ASME B1.15-1995 (R2003) | Unified Inch Screw Threads (UNJ Thread Form) | V Thread Form | |
| ASME B1.20.1-2013 | Pipe Threads, General Purpose (Inch) | Pipe Thread Form | |
| ANSI B1.20.3-1976 (R2013) | Dryseal Pipe Threads (Inch) | Pipe Thread Form | |
| ASME B1.20.7-1991 (R2013) | Hose Coupling Screw Threads - Inch | Pipe Thread Form | |
| ASME B1.21M-1997 (R2013) | Metric Screw Threads - MJ Profile | V Thread Form | |
| BS 84 | Tables of BS Whitworth, BS Fine and BS Pipe Threads | V Thread Form (55°) | 1⁄4″-20 BSW |
| ISO 68-1:1998 | ISO general purpose screw threads—Basic profile—Part 1: Metric screw threads | V Thread Form | |
| ISO 68-2:1998 | ISO general-purpose screw threads—Basic profile—Part 2: Inch screw threads | V Thread Form | |
| ISO 261:1998 | ISO general purpose metric screw threads—General plan | V Thread Form | M6x1 |
| ISO 262:1998 | ISO general purpose metric screw threads—Selected sizes for screws, bolts and nuts | V Thread Form | |
| ISO 724:1993 | ISO general-purpose metric screw threads—Basic dimensions | V Thread Form | |
| ISO 725:2009 | ISO inch screw threads—Basic dimensions | V Thread Form 51386 | |
| DIN 40400 | Edison Thread | Round V Thread Form |
| Standard | Name | Type | Obsolescence date |
|---|---|---|---|
| BS 93:1951 | British Association (B.A.) screw threads with tolerances for sizes 0 B.A. to 16 B.A. | 1966[2] | |
| BS 93:2008 | British Association (B.A.) screw threads | 1966[3] |