Identify any fastener with 1:1 precision.

How to Measure Screw Size with 1:1 Accuracy

To understand how to measure screw size correctly, you need to determine three key dimensions: the major diameter, the overall length, and the thread pitch.

• Major Diameter: This is the thickness of the threaded shank. Laying your bolt on our actual size screw gauge will show you if you are dealing with a standard metric size like an m6 bolt size (6.0 mm) or an imperial size like a #10 screw diameter (0.190 inches / 4.83 mm).
• Fastener Length: Different screws are measured differently. For countersunk screws, the length is measured from the very top of the head. For pan, round, or socket cap screws, the length is measured from under the head. Our digital caliper makes it easy to slide and match these lengths.
• Thread Pitch: The pitch is the distance between threads (metric) or the number of threads per inch (TPI, imperial). Our interactive screw thread pitch gauge helps you match these profiles crest-for-crest.

Using the Digital Bolt Size Identifier

Traditional metric screw size charts can be hard to read, and physical thread checkers are easy to lose. Our digital bolt size identifier combines a virtual vernier caliper and a database of standard screw sizes to give you instant results. Simply calibrate your screen using a credit card or a coin, place your fastener on the screen, and slide the jaws. The tool automatically compares the measurements and tells you the closest matches, showing you the exact designation (e.g., M5 x 0.8 Coarse or #8-32 UNC).

Identifying Machine Screw Sizes vs. Wood Screw Sizes

Screws are generally categorized by their application:

• Machine Screw Sizes: These fasteners have uniform, fine threads designed to go into pre-tapped holes or nuts. They require a highly precise match. For example, an m6 bolt size requires an M6 nut with a matching 1.0mm pitch.
• Wood Screw Sizes: These have pointed tips and coarse, sharp threads designed to cut directly into wood or plastic. They do not require a nut and have larger tolerances.

Using our built-in screw head type identifier, you can also classify the head style (countersunk, pan, socket, or hex) and the drive system (Phillips, slotted, Allen, or Torx) to find the exact replacement part.

Printable Screw Gauge for Your Workbench

When you are working in a dusty garage or workshop, you might not want to place greasy screws on your phone or laptop screen. That is why we created a printable screw gauge cheat sheet. You can download and print this sheet on standard A4 or Letter paper. It contains a 1:1 scale ruler, circular diameter checkers, and thread pitch matching strips. It is the perfect paper-based companion for any workbench. Always make sure to print at 1:1 scale (no scaling / actual size) and verify using a credit card on the printed alignment box.