How to tell if bolt is metric or standard?
Determining whether a bolt is metric or standard (also known as SAE or imperial) is crucial when working on projects that require specific hardware. Incorrectly using the wrong type of bolt can lead to problems with fit, strength, and safety. Here's a quick guide on how to identify the bolt type.
Identifying Metric vs. Standard Bolts
The easiest way to tell if a bolt is metric or standard is to look at the thread pattern. Metric bolts have a finer, more closely spaced thread pattern compared to standard bolts. You can also check the head size and diameter of the bolt shank:
- Metric bolts typically have a head size in millimeters (e.g. M8, M10) and the bolt diameter is also measured in millimeters.
- Standard (SAE) bolts have a head size in fractions of an inch (e.g. 1/4", 3/8") and the diameter is measured in inches.
Another visual cue is the presence of markings on the bolt head. Metric bolts often have the bolt diameter stamped on the head, while standard bolts may have a "SAE" or "USS" marking.
Using a Bolt Gauge
If you're still unsure, you can use a bolt gauge or thread pitch gauge to measure the thread pattern. These tools allow you to quickly compare the bolt to standard metric and SAE thread sizes to determine the correct type.
- Slide the bolt into the appropriate slot on the gauge.
- The slot that best matches the thread pitch will indicate if the bolt is metric or standard.
Knowing how to properly identify bolt types is an essential skill for any DIYer or mechanic. Taking the time to inspect the bolt closely can save you from costly mistakes down the road.
