Understanding Thread - How Read Thread for National Unified Threads (UNC, UNF, UNEF, UN) by Yatin Manchanda

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A Guide to Thread Standards – How to Interpret American Thread Designation Written by: johnsinit • Edited by: Lamar Stonecypher Published Sep 29, 2009 • Related Guides: ISO | UN How to read thread specifications? What does 2-56 UNF- 2B mean? What is the difference between the DIN and the UN standards? What does "LH" stands for in thread designation? Read this helpful article and get the answer to these questions.

Introduction As was already covered in the first part of the thread standard series, there are numerous thread standards used in different countries. ISO threads (designated according to DIN standard) are used in Europe and have metric dimensions, as also those of UK (BSP standards). The UNC-UNF threads are dimensioned in inches and are used in American-developed systems. There are also more exotic threads – like UNJF and NPT (used in pipe systems). Every thread is designated according to certain rules – and in this article we will provide an overview of these rules.

American Standard Thread Designations Major American standards use the following code: DD-PP-SS-XA/B-(LH) DD is the major diameter of the thread. Thus 3/8-inch thread will have a 3/8 standing at the left most of the thread specification. The dimensions usually come at margins of an inch (1/2, ¼, 1/8 ,1/16 etc). It must be noted that threads with a diameter smaller than ¼ have been given special numbers, from 0 to 10.

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PP stands for number of threads per inch. Thus, -20 means that there are 20 threads in each inch along the thread. SS is the thread standard. Mostly, it is defined by the diameter and number of coils, but sometimes there are several standards (such as UNC and UNJC) that use the same numbers. Thus, this should not be omitted – also helping to prevent errors. If you will write ¼-30 –UNF beside your thread, anyone looking at this will note that something is wrong, as Unified National Fine standards defines 28 threads per inch.

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X is the level of closing between the male and female thread, called class. 1 is the most loose thread, meaning there is less contact between threads and more clearance. 2 is the most common class and 3 is the most precise fit, used in accurate applications. A or B is used to specify whether it is an external or internal thread. External thread is designated A and internal – B. LH is used to specify the unusual left hand – used sometimes for locking against rotational force or other special applications. MOST POPULAR ARTICLES How to Select a Correctly Size Steel I Beam? Shaft Couplings - Types Types and Designs of Shaft Keys How to Perform Assembly Tolerance Stack Up Analysis by Worst Case Method Five Hydraulic Component Symbols You Should Learn Before Reading or Designing

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So, after reading the above paragraph, you should know that:

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2-56 UNF 2A means it is a #2 thread (sometimes called also 0.086, as this is 0.086 inch) with 56 threads per inch, manufactured, dimensioned and checked according to Unified National Fine Standard and this is a normal external thread.

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¼ -20 – UNC -3B –LH means this is a ¼ inch diameter thread with 20 thread per inch, manufactured in accordance with Unified National Coarse Standard. The thread is internal and precise and also left handed. 7/8 – 20 – UNEF -2B stands for internal normal precision thread with a diameter of 7/8 inch and 20 threads per inch, which is Unified National Extra Fine Standard. NEXT ARTICLE

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Overview of Thread Standards – Part One Written by: johnsinit • Edited by: Lamar Stonecypher Published Sep 18, 2009 • Related Guides: ISO | UN There are many types of thread standards depending on the country and purposes. You have probably heard about ISO, UNF, and UNC. But there are more thread standards present – some used for specific purposes and some used in certain countries. Familiarize yourself with the topic by reading below.

Introduction There are many threads used in different applications. The standard ISO, UNC, UNF and other, the extra fine UNEF threads, used in delicate mechanisms, the NPT threads used in fittings, British BSF, and BSP. Here is a list of some most common threads: International Organization for Standardization (ISO) National Coarse (NC USA) Unified National Coarse (UNC USA) National Fine (NF USA)

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Unified National Fine (UNF USA)

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Unified National Extra Fine (UNEF USA), Unified National 8-, 12- and 16 pitch series (UN USA), Special Threads of American National Form (UNS USA), National Taper Pipe 1:16 (NPT USA), National Taper Pipe Dryseal 1:16 (NPTF USA), National Standard Straight Pipe (NPS USA), National Standard Straight Pipe for free fitting mechanical (NPSM USA)

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National Standard Internal Straight Pipe Dryseal (NPSF USA) British Standard Withworth Coarse (BSW) British Standard Fine (BSF) British Standard Pipe (BSP) British Standard Pipe Taper (BSPT)

Similar yet Different While most American and European international standard threads use a thread angle of 60 degrees, various types of thread standards available in Great Britain have a thread angle of 55 degree. MOST POPULAR ARTICLES

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Sometimes the specifications and standards are complementary or supplementary. For example UNC, the Unified Coarse Thread is very much comparable with the ISO metric standard, and those can sometimes be used together.

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Thread Data

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The data for each standard thread should contain the following features: Incline angle – is the angle formed by the two adjacent flanks.

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Pitch – is the distance from one thread groove to the next.

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Pitch diameter – It is defined as the measured length between the pitch points taken in the groove between the threads. This is an important measure of the quality. There are also major and minor diameters that can be calculated from the pitch diameter and the incline angle.

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Tolerance – is the limit of the acceptable deviation from the intended design to the manufactured threads. This is very important for testing purposes done in various ways. One of the important methods to assure the quality standards is gauging inspection. This is the physical inspection of the thread for the features using a device with an established standard size. The result of the gauging inspection will be a pass/fail or go-no go condition. Depth of a thread - is the length of the space measured between the base and the top. This is the distance from the crest to the base of the root. The thread name is usually a combination of the above data. Understanding thread specifications will be covered in the next article.

Thread Standards

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Guide to Fasteners - Part I - Overview of Bolts and Screws Written by: johnsinit • Edited by: Lamar Stonecypher Published Apr 1, 2009 Bolts and screws are commonly used fasteners to keep the machine parts together. There are many different types of bolts and screws – varying types of heads, threads and more. Different versions are used depending on the application requirement.

Introduction Many people know that without fasteners like screws, bolts and nuts, no industry can survive. These are the basic hardware parts required by any machines, whether simple household items to complex high-end machines in industries. It is many times essential to use high quality nuts, bolts and screws. From small furniture crafting to oil sector industries the most essential hardware items include these fasteners – bolted joint is the most trustworthy part connection – moreover, it usually gives an option of dismantling and reinstalling. Anyway, the generalization and systematization process and the most modern technological advancements have changed the field of fasteners for the best.

Materials One of primary feature used by most of the machines is threaded joint as part of the design. The bolted joint can hold severe loads and the parts can be separated and reconnected repeatedly. Today, these fasteners are available in different materials like stainless steal, copper, brass and alloy steels. With the advancement of the technologies even porcelain and glasses are used as screws for many applications including canning jars and electrical insulators.

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Bolt vs Screw Though many times confused by amateurs, bolts and screws are different types of fasteners. Bolts are headed fasteners with external threads suitable for non-tapered nut. They require a nut (or some other thread) as a counter - to lock the joint. The bolts are made with uniform threads satisfying the standard specifications such as UNJ, UNR, MJ etc. and are used in most industrial applications – secured with a spring-washer or a locktite. To sum it up, bolts are designed to use as a fastener placed through already drilled holes in the machine parts and these requires a nut to tighten it from the other end.

Screws are headed externally threaded types of fasteners without meeting the standard specifications of the bolts. They are shafts with provision at one end to turn the screw and have a helical thread on its surface, which is capable of piercing strongly into the surface. They do not require a nut and are used mostly in home-based application – such a connecting a picture to the wall. It is actually the simplest example of converting torque into linear force.

Head types Depending up on the design of the heads the screws/bolts are named differently. Pan head is a low disc with chamfered outer edge. Hexagon head bolts are generally used for bigger loads. Socket head is a cylinder with (usually) Hex socket (Allen) opening – those bolts usually have the smallest head. Flat head or countersunk screws are conically shaped with tapering inner face and flat outer face. It will allow the screw to sink into the material – providing “flat surface”. There are also many special types of bolts with different heads including oval or raised head, bugle head, cheese head. Even square head screws are present – as well as there are headless screws and bolts.

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