Home » Informazioni su » How to measure a screw
How to measure a screw

How to measure a screw

Different types of screws are measured in slightly different ways, depending on factors like their head shape, thread type, and intended use. Here’s our explanation for how to measure screws:

1. Screw Length

  • Flathead screws are measured from the top of the head to the tip, because the entire head sinks into the material.
  • Pan head, round head, or hex head screws are measured from just under the head to the tip, since the head stays above the material.
  • Countersunk screws follow the same rule as flatheads, where the entire length is considered part of the measurement.

The key difference lies in whether the head of the screw remains above or sinks into the material, which changes how you measure its full length.

2. Diameter

The diameter is measured across the shank (the threaded portion) of all screws, but the way it’s presented differs:

  • Metric screws are measured in millimetres across the outer edges of the threads (the major diameter).
  • Imperial screws are typically categorised by a gauge number or by fractional inch sizes. Using a caliper gives a precise reading of the diameter in either system.

The tool used (like a caliper) stays the same across different types, but the units of measurement vary.

3. Thread Pitch

Thread pitch can be measured differently:

  • Metric screws are measured by the distance between threads (in millimetres), while
  • Imperial screws are measured by threads per inch (TPI). Both require a thread pitch gauge or counting threads over a set distance, but the units and method of reading differ.

4. Head and Drive Types

Though the way you measure length, diameter, and thread pitch can vary, the head type (like flat, round, or hex) and the drive type (Phillips, slotted, or Torx) don’t affect measurement directly. Instead, they influence which tools are needed for installation and how the screw fits into a material.

In summary, while the core principles of measuring screws (length, diameter, thread pitch) remain consistent, the method of measuring and the tools needed can vary based on the screw type and application.