Measuring a hex head screw primarily involves determining its key dimensions, most notably its length, but also diameter and thread pitch.
The most common way to measure a hex head screw, often referred to as a hex head cap screw, is by its length. Unlike some other fastener types that are measured from the top of the head, a hex head screw is measured from the bearing surface (the flat surface underneath the head) to the tip of the threads.
Here are the key measurements you typically take for a hex head screw:
1. Length
- Where to Measure: Place the screw against a ruler or measuring tape. The measurement starts from the underside of the hex head (the bearing surface that sits flush against the material) and extends straight down to the very end of the screw's tip.
- What to Use: A ruler, measuring tape, or calipers are standard tools. Calipers provide greater precision, especially for smaller screws.
- Measurement Point: Always measure from the flat bearing surface beneath the head, not the top of the head itself.
2. Diameter
- Where to Measure: The diameter is measured across the threaded portion of the screw.
- What to Use: Use calipers to measure the major diameter, which is the largest diameter of the screw threads. Measure across the threads, not in between them.
- Measurement Point: Measure perpendicular to the screw's length.
3. Thread Pitch/Count
- What it is: This describes the coarseness or fineness of the threads.
- Imperial (Inch): Measured as threads per inch (TPI). You can count the number of threads within a one-inch section.
- Metric: Measured as the distance between adjacent threads (pitch, in millimeters).
- What to Use: A thread gauge (or thread pitch gauge) is the easiest tool for this.
- How to Use: Place the leaves of the thread gauge against the screw threads until you find the leaf that perfectly matches the thread profile.
Other Measurements
While length, diameter, and thread pitch are standard, other specific measurements might be taken depending on the application.
According to the provided reference, one might measure "lg link grip" using a thread gauge against the bearing surface. The distance between the end or flat of the thread gauge and the bearing surface represents this "lg link grip" measurement. The reference notes there is a "transition in between here and that's the difference," suggesting this measurement relates to a specific portion of the screw's length, possibly the unthreaded portion or the grip length relevant to thread engagement.
By accurately measuring these dimensions, you can identify or specify the correct hex head screw for your needs.
