With the Camcut thread table, you can easily find the dimensions of threads conforming to various standards. In addition to major and minor diameters, the tables also include pitch diameters and other dimensional data important for manufacturing for the most common thread standards.
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THREADS
A thread is defined by the thread standard used, the nominal thread diameter, and the thread pitch. The pitch is the distance between the crests of two consecutive threads, measured parallel to the thread centerline. In other words, the pitch indicates how far the screw advances along the centerline during one revolution. The terms “standard thread” and “fine thread” are widely established, although standard and fine threads are also referred to as coarse and fine threads.
Threads can be produced by cutting or forming, for example with a forming (roll) tap or thread mill, or by turning. External threads can also be made using high-speed-steel threading dies, but nowadays this method is used mainly for cleaning and restoring threads.
Threads are used for various purposes, such as fastening, moving components, or making adjustments. Threads are most commonly found on bolts and nuts. The most common function of bolts is to hold various assembled structures together, and a bolted joint must withstand the load for which it was designed.
Today, the most common bolt is an ISO metric 8.8 hexagon-head bolt. The bolt head usually bears only the numerical designation of the bolt’s strength class. The metric M thread is part of the general SI measurement system. In the strength-class designation marked on bolts, the first number before the decimal point indicates one hundredth of the nominal tensile strength in N/mm2. For example, the designation 8 means 800 N/mm2. The number after the decimal point indicates, multiplied by ten, the ratio between the lower yield strength ReL (or the 0.2% proof strength Rp0,2) and the nominal tensile strength Rm. Strength classes used for metric threads include 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, and 12.9. When the screw size, strength class, and other technical properties are known, the load it can withstand without damage can be calculated, and the required tightening torque can be determined. Socket-head cap screws are generally made of alloy steel, which is why they are often used in applications requiring higher strength. The most common strength classes for socket-head cap screws are 10.9 and 12.9.
The markings on stainless-steel bolts differ from those used on steel bolts. The first part of the designation consists of a letter and a number identifying the type of steel. For example, in A4, the A indicates austenitic steel, while the following number indicates one-tenth of the minimum tensile strength (N/mm2).
The inch-based UN thread standard is divided into coarse and fine threads, just like metric threads. The designation UNC (Unified Coarse) is used for coarse threads, while UNF (Unified Fine) identifies fine threads. These designations are also marked on the hexagonal heads of bolts. The bolt head also carries the strength-class marking, shown as radial lines. On nuts, the marking may consist of short lines on one side of the edge or a ring. Inch-based bolts have strength classes from 1 to 8, of which class 5 is the most commonly used. It is marked by three radial lines on the bolt head and corresponds approximately to strength class 8.8 for a metric-thread bolt. Sometimes a UN bolt head may also bear a single letter—S, T, or V—which is a British strength-class designation; S corresponds to class 5.
Calipers and thread pitch gauges are typically used to identify threads. The caliper is used to measure the external or internal diameter of the thread, while the thread pitch gauge determines the thread profile and pitch. Based on this information, the type of thread can be identified. The measuring instruments most commonly used in thread manufacturing are thread micrometers and thread calipers, which are used to measure the pitch diameter of the thread. In high-volume production, thread gauges are also used to verify that the thread meets the requirements specified by the upper and lower limit dimensions.
In addition to external and internal diameters, the Camcut thread tables provide pitch diameters and other dimensional data important for manufacturing for the most common thread standards, including ISO metric coarse and fine threads (ISO 261 and SFS-ISO 965-1), MJ threads (ISO 5855), inch-based UNC, UNF, and UNEF threads (ASME/ANSI B1.1), G, BSF, Whitworth, and NPT pipe threads (SFS-ISO 288-1 and ANSI/ASME B1.20.1), Tr trapezoidal threads (DIN 103 and ISO 2904), Rd round threads (DIN 405-1 and DIN 20400), PG conduit threads (DIN 40430), BA threads, and S threads (DIN 513).
