Bolts vs Screws: Choosing the Right Fastener

Bolts and screws look similar, and the terms are often used interchangeably. But they work differently, and choosing the right one makes a real difference to how a joint performs.

The difference

• A bolt passes through clearance holes in the parts and is tightened with a nut. The clamping force comes from the bolt being stretched. Bolts suit heavy loads and joints that need to come apart.
• A screw threads directly into the material, or into a tapped hole, and holds by its own thread. Self-drilling and self-tapping screws make their own hole or thread, which speeds up work in sheet metal and roofing.

Fully or partially threaded?

• Fully threaded fasteners have thread along the whole shank. They suit shorter lengths and applications where the full length must grip.
• Partially threaded fasteners have a plain shank under the head. The plain section is stronger in shear and gives a tighter, more accurate fit where the joint carries sideways loads.

Can you reuse screws?

Sometimes, but with care. Threads wear, coatings get damaged and heads deform each time a screw is driven. Reuse is acceptable for light, non-critical fixings if the thread and head are in good condition. For structural joints, high-tensile bolts, self-drilling screws and anything safety-critical, use new fasteners.

Dealing with a stripped screw

A stripped screw is usually caused by the wrong driver bit, too much torque or a worn head. Prevent it by using the correct bit size, setting the right torque on the driver, and keeping the driver straight. Once stripped, the screw may need to be extracted with a screw extractor and replaced, and the hole may need a larger screw or a thread insert. Overdriving is also a common cause of failure.

Avlock’s hardware range includes self-drilling and self-tapping screws, roofing screws and cup square bolts and nuts.