The gauge of a screw refers to its diameter, specifically the thickness of the un-threaded part known as the shank. It is a system used to specify the size of screws, primarily for smaller diameters.
Gauge is a numbered system rather than a direct measurement in inches or millimeters for most sizes. A higher gauge number indicates a larger screw diameter. This system is commonly used for wood screws, machine screws, and sheet metal screws.
Understanding Screw Gauge
Unlike larger screws that might be specified by their actual diameter (e.g., 1/4 inch), smaller screws use the gauge number. The number corresponds to a specific diameter according to standardized charts.
- The Shank: As defined by the reference, the gauge is determined by the thickness (diameter) of the un-threaded part of the screw known as the shank. This is the solid core of the screw before the threads begin or below the head on a partially threaded screw.
- Diameter: While the gauge is a number, it directly correlates to the screw's major diameter (the largest diameter including the threads, or the shank diameter on unthreaded or partially threaded screws).
- Standardization: Screw gauge standards exist (like ANSI/ASME standards in the US) to ensure consistency, although slight variations can occur between screw types or manufacturers.
Common Screw Gauge to Diameter Conversions
Understanding the actual diameter is crucial for selecting the correct drill bit size for pilot holes or choosing compatible nuts or washers. Below is a table showing common screw gauges and their approximate corresponding diameters in inches:
| Screw Gauge (#) | Approximate Diameter (Inches) | Approximate Diameter (mm) |
|---|---|---|
| #0 | 0.060 | 1.5 |
| #1 | 0.073 | 1.8 |
| #2 | 0.086 | 2.2 |
| #3 | 0.099 | 2.5 |
| #4 | 0.112 | 2.8 |
| #5 | 0.125 | 3.2 |
| #6 | 0.138 | 3.5 |
| #7 | 0.151 | 3.8 |
| #8 | 0.164 | 4.1 |
| #9 | 0.177 | 4.5 |
| #10 | 0.190 | 4.8 |
| #12 | 0.216 | 5.5 |
| #14 | 0.242 | 6.1 |
Note: Diameters are approximate and can vary slightly based on screw type and standard.
Why Screw Gauge Matters
Choosing the correct screw gauge is important for several reasons:
- Holding Power: A larger gauge (and thus diameter) generally provides more strength and holding power.
- Compatibility: Gauge ensures compatibility with pre-drilled holes, countersinks, and mating parts like nuts or washers.
- Application: Different applications require different gauges. For instance:
- Small electronics might use #0 or #2 screws.
- General woodworking often uses #8 or #10 screws.
- Construction framing might use larger diameter screws or nails.
In summary, the gauge is a standard sizing method for screw diameters, primarily based on the shank thickness, helping users select the appropriate fastener for their specific needs.
