The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wide variety of other threaded fasteners used in these countries. It has the same 60° profile as the ISO metric screw thread, but the characteristic dimensions of each UTS thread (outer diameter and pitch) were chosen as an inch fraction rather than a millimeter value. The UTS is currently controlled by ASME/ANSI in the United States.
Each thread in the series is characterized by its major diameter Dmaj and its pitch, P. UTS threads consist of a symmetric V-shaped thread. In the plane of the thread axis, the flanks of the V have an angle of 60° to each other. The outermost 1⁄8 and the innermost 1⁄4 of the height H of the V-shape are cut off from the profile.
The pitch P is the distance between thread peaks. For UTS threads, which are single-start threads, it is equal to the lead, the axial distance that the screw advances during a 360° rotation. UTS threads do not usually use the pitch parameter; instead a parameter known as threads per inch (TPI) is used, which is the reciprocal of the pitch.
The relationship between the height H and the pitch P is found using the following equation where is half the included angle of the thread, in this case 30 degrees:
In an external (male) thread (e.g., on a bolt), the major diameter Dmaj and the minor diameter Dmin define maximum dimensions of the thread. This means that the external thread must end flat at Dmaj, but can be rounded out below the minor diameter Dmin. Conversely, in an internal (female) thread (e.g., in a nut), the major and minor diameters are minimum dimensions, therefore the thread profile must end flat at Dmin but may be rounded out beyond Dmaj.
The minor diameter Dmin and effective pitch diameter Dp are derived from the major diameter and pitch as
The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch. For diameters smaller than 1⁄4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.
This number pair is optionally followed by the letters UNC, UNF or UNEF (Unified) if the diameter-pitch combination is from the coarse, fine, or extra fine series, and may also be followed by a tolerance class.
Example: #6-32 UNC 2B (major diameter: 0.1380 inch, pitch: 32 tpi)
A simplified formula to find the major diameter is: #of screw 6 x 0.013 +0.060 = 0.138
(inch / mm)
|Thread density (d, threads per inch) and thread pitch (p)||Preferred cutting tap drill size|
|Coarse (UNC)||Fine (UNF)||Extra fine (UNEF)|
|d (TPI)||p (inch / mm)||d (TPI)||p (inch / mm)||d (TPI)||p (inch / mm)||Coarse||Fine||Extra fine|
|#0||0.0600 / 1.5240||None||80||0.012500 / 0.3175||None||3⁄64 in (.047)|
|#1||0.0730 / 1.8542||64||0.015625 / 0.3969||72||0.013888 / 0.3528||None||#53 (.060)||#53 (.060)|
|#2||0.0860 / 2.1844||56||0.017857 / 0.4536||64||0.015625 / 0.3969||None||#50 (.070)||#50 (.070)|
|#3||0.0990 / 2.5146||48||0.020833 / 0.5292||56||0.017857 / 0.4536||None||#47 (.079)||#45 (.082)|
|#4||0.1120 / 2.8448||40||0.025000 / 0.6350||48||0.020833 / 0.5292||None||#43 (.089)||#42 (.094)|
|#5||0.1250 / 3.1750||40||0.025000 / 0.6350||44||0.022727 / 0.5773||None||#38 (.102)||#37 (.104)|
|#6||0.1380 / 3.5052||32||0.031250 / 0.7938||40||0.025000 / 0.6350||None||#36 (.107)||#33 (.113)|
|#8||0.1640 / 4.1656||32||0.031250 / 0.7938||36||0.027778 / 0.7056||None||#29 (.136)||#29 (.136)|
|#10||0.1900 / 4.8260||24||0.041667 / 1.0583||32||0.031250 / 0.7938||None||#25 (.150)||#21 (.159)|
|#12||0.2160 / 5.4864||24||0.041667 / 1.0583||28||0.035714 / 0.9071||32||0.031250 / 0.7938||#16 (.177)||#14 (.182)||3⁄16 in (.188)|
|1⁄4″||0.2500 / 6.3500||20||0.050000 / 1.2700||28||0.035714 / 0.9071||32||0.031250 / 0.7938||#7 (.201)||#3 (.213)||7⁄32 in (.219)|
|5⁄16″||0.3125 / 7.9375||18||0.055556 / 1.4111||24||0.041667 / 1.0583||32||0.031250 / 0.7938||F (.257)||I (.272)||9⁄32 in (.281)|
|3⁄8″||0.3750 / 9.5250||16||0.062500 / 1.5875||24||0.041667 / 1.0583||32||0.031250 / 0.7938||5⁄16 in (.313)||Q (.332)||11⁄32 in (.344)|
|7⁄16″||0.4375 / 11.1125||14||0.071428 / 1.8143||20||0.050000 / 1.2700||28||0.035714 / 0.9071||U (.368)||25⁄64 in (.391)||Y (.404)|
|1⁄2″||0.5000 / 12.7000||13||0.076923 / 1.9538||20||0.050000 / 1.2700||28||0.035714 / 0.9071||27⁄64 in (.422)||29⁄64 in (.453)||15⁄32 in (.469)|
|9⁄16″||0.5625 / 14.2875||12||0.083333 / 2.1167||18||0.055556 / 1.4111||24||0.041667 / 1.0583||31⁄64 in (.484)||1⁄2 in (.5)||33⁄64 in (.516)|
|5⁄8″||0.6250 / 15.8750||11||0.090909 / 2.3091||18||0.055556 / 1.4111||24||0.041667 / 1.0583||17⁄32 in (.531)||9⁄16 in (.563)||37⁄64 in (.578)|
|3⁄4″||0.7500 / 19.0500||10||0.100000 / 2.5400||16||0.062500 / 1.5875||20||0.050000 / 1.2700||21⁄32 in (.656)||11⁄16 in (.688)||45⁄64 in (.703)|
|7⁄8″||0.8750 / 22.2250||9||0.111111 / 2.8222||14||0.071428 / 1.8143||20||0.050000 / 1.2700||49⁄64 in (.766)||51⁄64 in (.797)||53⁄64 in (.828)|
|1″||1.0000 / 25.4000||8||0.125000 / 3.1750||12 [a]||0.083333 / 2.1167||20||0.050000 / 1.2700||7⁄8 in (.875)||59⁄64 in (.922)||61⁄64 in (.953)|
The following formula is used to calculate the major diameter of a numbered screw greater than or equal to 0: Major diameter = Screw # × 0.013 in + 0.060 in. For example, a number 10 calculates as: #10 × 0.013 in + 0.060 in = 0.190 in major diameter. To calculate the major diameter of "aught" size screws count the number of extra zeroes and multiply this number by 0.013 in and subtract from 0.060 in. For example, the major diameter of a 0000 screw thread is 0.060 in − (3 × 0.013 in) = 0.060 in − 0.039 in = 0.021 in.
The number series of machine screws has been extended downward to include #00-90 (0.047 in = 0.060 in − 0.013 in) and #000-120 (0.034 in = 0.060 in − 2 × 0.013 in) screws; however, the main standard for screws smaller than #0 is ANSI/ASME standard B1.10 Unified Miniature Screw Threads. This defines a series of metric screws named after their major diameters in millimetres, from 0.30 UNM to 1.40 UNM. Preferred sizes are 0.3, 0.4, 0.5, 0.6, 0.8, 1.0 and 1.2 mm, with additional defined sizes halfway between. :1861 The standard thread pitch is approximately 1/ of the major diameter. The thread form is slightly modified to increase the minor diameter, and thus the strength of screws and taps. The major diameter still extends to within 1/H of the theoretical sharp V, but the total depth of the thread is reduced 4% from 5/H = 5/ cos(30°) P ≈ 0.541P to 0.52P. :1858–1859 This increases the amount of the theoretical sharp V which is cut off at the minor diameter by 10% from 0.25H to 7/ − 0.52/ ≈ 0.27456H.
The number series of machine screws once included more odd numbers and went up to #16 or more. Standardization efforts in the late 19th and the early part of the 20th century reduced the range of sizes considerably. Now, it is less common to see machine screws larger than #14, or odd number sizes other than #1, #3 and #5. Even though #14 and #16 screws are still available, they are not as common as sizes #0 through #12.[ citation needed ]
Sometimes "special" diameter and pitch combinations (UNS) are used, for example a 0.619 in (15.7 mm) major diameter with 20 threads per inch. UNS threads are rarely used for bolts, but rather on nuts, tapped holes, and threaded ODs. Because of this UNS taps are readily available. Most UNS threads have more threads per inch than the correlating UNF or UNEF standard; therefore they are often the strongest thread available. Because of this they are often used in applications where high stresses are encountered, such as machine tool spindles or automotive spindles.
A screw thread gauging system comprises a list of screw thread characteristics that must be inspected to establish the dimensional acceptability of the screw threads on a threaded product and the gauge(s) which shall be used when inspecting those characteristics.
Currently this gauging for UTS is controlled by:
This Standard provides essential specifications and dimensions for the gauges used on Unified inch screw threads UN [unified] and UNR [external threads only] thread form, and covers the specifications and dimensions for the thread gauges and measuring equipment listed in Tables 1 and 2. The basic purpose and use of each gauge are also described.
(a) This Standard presents screw thread gauging systems suitable for determining the acceptability of Unified [UN], UNR [external threads only], UNJ [internal and external threads], M, and MJ screw threads on externally and internally threaded products. It establishes the criteria for screw thread acceptance when a gauging system is used. (b) A screw thread gauging system comprises a list of screw thread characteristics that must be inspected to establish the dimensional acceptability of the screw threads on a threaded product and the gauge(s) which shall be used when inspecting those characteristics. (c) Federal Government Use. When this Standard is approved by the Department of Defense and federal agencies and is incorporated into Federal Standard-H28/20 [FED-STD-H28/20], Screw Thread Standards for Federal Services, Section 20, the use of this Standard by the federal government is subject to all the requirements and limitations of Federal Standard-H28/20 [FED-STD-H28/20]. These standards provide essential specifications and dimensions for the gauges used on Unified inch screw threads (UN, UNR, UNJ thread form) on externally and internally threaded products. It also covers the specifications and dimensions for the thread gauges and measuring equipment. The basic purpose and use of each gauge are also described. It also establishes the criteria for screw thread acceptance when a gauging system is used.
A classification system exists for ease of manufacture and interchangeability of fabricated threaded items. Most (but certainly not all) threaded items are made to a classification standard called the Unified Screw Thread Standard Series. This system is analogous to the fits used with assembled parts.
The letter suffix "A" or "B" denotes whether the threads are external or internal, respectively. Classes 1A, 2A, 3A apply to external threads; Classes 1B, 2B, 3B apply to internal threads.
Thread class refers to the acceptable range of pitch diameter for any given thread. The pitch diameter is indicated as Dp in the figure shown above. There are several methods that are used to measure the pitch diameter. The most common method used in production is by way of a go/no-go gauge.
A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for accurate measurement of components in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers. Micrometers are usually, but not always, in the form of calipers. The spindle is a very accurately machined screw and the object to be measured is placed between the spindle and the anvil. The spindle is moved by turning the ratchet knob or thimble until the object to be measured is lightly touched by both the spindle and the anvil.
American National Standard Pipe Thread standards, often called national pipe thread (NPT) standards for short, are U.S. national technical standards for screw threads used on threaded pipes and pipe fittings. They include both tapered and straight thread series for various purposes including rigidity, pressure-tight sealing, or both. The various types are each named with a symbol and a full name; examples of the symbols include NPT, NPS, NPTF, NPSC, and others.
A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a bolt or nut. Other uses are as a spacer, spring, wear pad, preload indicating device, locking device, and to reduce vibration. Washers often have an outer diameter (OD) about twice their inner diameter (ID), but this can vary quite widely.
Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the mating of screw threads.
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 a ridge 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. A screw thread is the essential feature of the screw as a simple machine and also as a threaded fastener.
British Standard Whitworth (BSW) is an imperial-unit-based screw thread standard, devised and specified by Joseph Whitworth in 1841 and later adopted as a British Standard. It was the world's first national screw thread standard, and is the basis for many other standards, such as BSF, BSP, BSCon, and BSCopper.
British Association screw threads, or BA screw threads, are a largely obsolete set of small screw threads, the largest being 0BA at 6 mm diameter. They were, and to some extent still are, used for miniature instruments and modelling.
A garden hose, hosepipe, or simply hose is a flexible tube used to convey water. There are a number of common attachments available for the end of the hose, such as sprayers and sprinklers. Hoses are usually attached to a hose spigot or tap.
Trapezoidal thread forms are screw thread profiles with trapezoidal outlines. They are the most common forms used for leadscrews. They offer high strength and ease of manufacture. They are typically found where large loads are required, as in a vise or the leadscrew of a lathe. Standardized variations include multiple-start threads, left-hand threads, and self-centering threads.
British Standard Brass or British Brass Thread is an imperial unit based screw thread. It adopts the Whitworth thread form with a pitch of 26 threads per inch and a thread angle of 55 degrees for all diameters. It is often wrongly called British Standard Brass but is not actually covered by a British Standard.
The ISO metric screw thread is the most commonly used type of general-purpose screw thread worldwide. They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947.
Edison screw (ES) is a standard lightbulb socket for electric light bulbs. It was developed by Thomas Edison, patented in 1881, and was licensed in 1909 under General Electric's Mazda trademark. The bulbs have right-hand threaded metal bases (caps) which screw into matching threaded sockets. For bulbs powered by AC current, the thread is generally connected to neutral and the contact on the bottom tip of the base is connected to the "live" phase.
Computer case screws are the hardware used to secure parts of a PC to the case. Although there are numerous manufacturers of computer cases, they have generally used three thread sizes. The Unified Thread Standard (UTS) originates from the United States, while the ISO metric screw thread is standardized worldwide. In turn, these thread standards define preferred size combinations that are based on generic units—some on the inch and others on the millimetre.
A screw and a bolt are similar types of fastener typically made of metal, and characterized by a helical ridge, known as a male thread. Screws and bolts are used to fasten materials by the engagement of the screw thread with a similar female thread in the matching part.
United States Standard thread, also known as Sellers Standard thread, Franklin Institute thread and American Standard thread, is a standard for inch based threaded fasteners and washers.
ISO 898 is an international standard that defines mechanical and physical properties for metric fasteners. This standard is the origin for other standards that define properties for similar metric fasteners, such as SAE J1199 and ASTM F568M. It is divided into five (nonconsecutive) parts:
The Swiss-designed Thury screw thread is a metric thread standard that was developed in the late nineteenth century for screws used in scientific and horological instruments. The thread is named after Marc Thury, an engineer and professor at the University of Geneva who contributed heavily to the standard's development.
Despite fire hose and hydrant coupler standardization efforts that are at least 144 years old, there remain significant areas in Canada, the United States, and Mexico that use fire hose and hydrant threads and other couplings that are incompatible with those used by neighboring fire departments. This is notable because the first fire hydrant was invented by Manhattan fire fighter George Smith in 1817, making these devices 200 years old.
Preferred metric sizes are a set of international standards and de facto standards that are designed to make using the metric system easier and simpler, especially in engineering and construction practices. One of the methods used to arrive at these preferred sizes is the use of preferred numbers and convenient numbers such as the Renard series, the 1-2-5 series to limit the number of different sizes of components needed.