Inch sized fasteners and more

Screw Determination

When identifying screws, several important factors can help you determine the type, size, and thread. On this page, you will learn how to identify screws based on their dimensions and thread types, as well as which tools can assist you. Use this information to accurately classify screws and ensure you choose the right fastener for your application.

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Guide to Screw Sizes and Types


Cylinder Screw similar to DIN 912, 1/4 20-UNC x 1.1/2

To determine the thread count, count the threads over one inch (25.4mm), or simply scale up for shorter threads. To convert the length to millimeters, multiply the inch length by 25.4 (for 1/4: 1 divided by 4 times 25.4 = 6.35mm).

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Thread Gauges

Thread gauges are a practical tool for determining the thread count of a screw. These gauges can be easily applied to the thread to measure the exact number of threads per inch. This allows you to quickly identify whether it is a UNC or UNF thread.

Example for Thread Gauges