2026 Complete In-Service Bridge Safety Inspection Practice Test

A versatile size tends to become the most popular because it works well for a wide range of everyday tasks. The 6 mm (about 1/4 inch) diameter hits that sweet spot: it’s sturdy enough for many general connections, easy to install with common tools, and is widely stocked by suppliers. That combination—adequate strength with broad availability and reasonable cost—makes it the default choice in many standard fastener applications. Smaller 4 mm fasteners are typically used only for light-duty work, while larger 8 mm or 10 mm sizes are chosen for heavier-duty, specialized applications, so they aren’t as universally common.