To download standard BS 3643-1:1981 ISO metric screw threads. Principles and basic data: Click the Download arrow icon. If the link fails, the document cannot be downloaded, please click on the Broken link to let us know. To view the content of other pages click on the transfer page Icon. Click the '+' sign icon to add this document to your. Gauges and gauging for ISO general purpose metric threads are defined in the ISO 1502:1996 standard. The basic profile of ISO general purpose metric screw threads is defined in the ISO 68-1:1998 and given in the first figure below. External (bolt) thread root profile is given the 'Definitions' section.
Thread stripping area for standard metric threadsThread stripping area for standard metric threads
Iâm looking for information on thread stripping area for standard metric threads.
Both Machineryâs Handbook and the Fasteners Standards Handbook of the Industrial Fastener Institute give the following formulae for the stripping area of threads of Unified (inch) thread form: External threads: ASs = 3.1416 * Le * Knmax * n * (0.5/n + 0.57735 * (Esmin â Knmax)) Where: ASs = stripping area of external thread, in.^2 Le = length of thread engagement, in. n = threads per in. Knmax = maximum minor diameter of internal thread, in. Esmin = minimum pitch diameter of external thread, in. Internal threads: ASn = 3.1416 * Le * Knmax * n * (0.5/n + 0.57735 * (Dsmin â Enmax)) Where: ASn = stripping area of internal thread, in.^2 Le = length of thread engagement, in. n = threads per in. Dsmin = minimum major diameter of external thread, in. Enmax = maximum pitch diameter of internal thread, in. Would these formulae apply to standard metric threads (with in. replaced by mm, of course)? If not, can you steer me to the right formulae? Or a table of values for thread stripping areas for metric threads? 0.57735 would appear to be tan(30 deg). 30 deg is the thread flank angle in both the Unified and metric systems. 3.1416 would appear to be pi. Last time I checked, pi was the same in both systems.
The ISO metric screw threads are the most commonly used type of general-purpose screw thread worldwide.[1] They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947.[citation needed]
The 'M' designation for metric screws indicates the nominal outer diameter of the screw, in millimetres (e.g., an M6 screw has a nominal outer diameter of 6 millimetres).
Basic profile[edit]
Basic profile of all ISO metric screw threads
The design principles of ISO general-purpose metric screw threads ('M' series threads) are defined in international standard ISO 68-1.[2] Each thread is characterized by its major diameter, D (Dmaj in the diagram), and its pitch, P. ISO metric 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 thread depth is 0.614 à pitch. The outermost â1â8 and the innermost â1â4 of the height H of the V-shape are cut off from the profile.
The relationship between the height H and the pitch P is found using the following equation where θ{displaystyle theta } is half the included angle of the thread, in this case 30 degrees:[3]
or
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
Designation[edit]
A metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (the maximum thread diameter for external thread and the minimum diameter for internal one) and the pitch P, both expressed in millimetres and separated by the hyphen sign, - (e.g., M8-1.25). If the pitch is the normally used 'coarse' pitch listed in ISO 261 or ISO 262, it can be omitted (e.g., M8). The length of a machine screw or bolt is indicated by a following x and the length expressed in millimetres (e.g., M8-1.25x30 or M8x30). Tolerance classes defined in ISO 965-1 can be appended to these designations, if required (e.g., M500â 6g in external threads).
External threads are designated by lowercase letter, g or h. Internal threads are designated by upper case letters, G or H.
Preferred sizes[edit]
ISO 261 specifies a detailed list of preferred combinations of outer diameter D and pitch P for ISO metric screw threads. The 1st choice column follows (approximately) the R10 series from ISO 3, while the 2nd choice column are rounded off values from the R20 series from ISO 3.[4][5][2]
ISO 262 specifies a shorter list of thread dimensions â a subset of ISO 261.[6]
The âcoarseâ pitch is the commonly used default pitch for a given diameter. In addition, one or two smaller âfineâ pitches are defined, for use in applications where the height of the normal âcoarseâ pitch would be unsuitable (e.g., threads in thin-walled pipes). The terms âcoarseâ and âfineâ have (in this context) no relation to the manufacturing quality of the thread.
In addition to coarse and fine threads, there is another division of extra fine, or âsuperfineâ threads, with a very fine pitch thread. Superfine pitch metric threads are occasionally used in automotive components, such as suspension struts, and are commonly used in the aviation manufacturing industry. This is because extra fine threads are more resistant to coming loose from vibrations.[7]
Spanner (wrench) sizes[edit]
Below are some common spanner (wrench) sizes for metric screw threads. Hex head widths (width across flats, spanner size) are for DIN 934 hex nuts and hex head bolts. Other (usually smaller) sizes may occur for reasons of weight and cost reduction.
Standards[edit]International[edit]
National[edit]
See also[edit]
References[edit]
Bibliography[edit]
External links[edit]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=ISO_metric_screw_thread&oldid=932704640'
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