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Select the screws according to the thread size

2023

Select the screws according to the thread size

2023-05-29

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The thread size consists of two parameters – outside diameter and pitch. The outside diameter is the maximum diameter of the thread. Pitch refers to the distance between adjacent threads.

In general, there are two international standards for thread sizes in the industry. One is UTS (Unified Thread Standard) and the other is ISO Metric (International Organization for Standardization Metric Screw Thread).

UTS: The outer diameter and pitch are represented by a set of codes, for example, # 4-40 or 1/4 "-20; both main parameters are measured in inches.
The first part of the code indicates the outer diameter, or a fraction if the outer diameter is greater than or equal to 0.25 inches; If it is less than 0.25 inches, add a number table with "#". The second part of the code represents the pitch, using the TPI (Threads Per Inch) value as the code. For example, Keystone Electronics' screw nail 9906. Its thread size is #8-32, with 8 referring to an outside diameter of 0.1640 inches and 32 referring to a distance of 0.03125 inches between adjacent threads.

ISO Metric
ISO Metric also uses a set of codes to represent the outside diameter and pitch. The main difference is that ISO Metric is measured in millimeters (mm) and the code is represented in Maa X bb, with aa for outer diameter and bb for pitch. For example, Hammond Manufacturing's 1591MS100 has a thread size of M3 x 0.5, which represents a 3mm OD x 0.5mm pitch.

Product recommendations: 1) Except for customized screws, all outside diameter and pitch matching are standardized in accordance with ISO Metric standards.
In some cases, the pitch of M3 screws is 0.5mm as standard. Some manufacturers simplify the expression of thread size to "M3".