Guide to Fixings: Screws, Bolts, and Anchors

The right fixing holds securely. The wrong one fails, sometimes dangerously. Here's how to choose appropriate fixings for common situations.

Wood Screws

Standard Wood Screws

Tapered thread, designed to cut into wood. Various head types:

• Countersunk - Sits flush with surface
• Round head - Sits proud, visible
• Pan head - Flat bottom, low profile

Drywall Screws

Fine thread, bugle head (self-countersinking). Specifically for plasterboard to timber. Not ideal for wood-to-wood.

Decking Screws

Corrosion resistant, designed for outdoor use. Often have cutting tips and specific thread patterns.

Coach Screws

Heavy-duty hex-head screws for structural connections. Need pilot holes.

Machine Screws and Bolts

Machine Screws

Uniform thread, designed for threaded holes or nuts. Various heads (pan, countersunk, cap, etc.).

Bolts

Larger versions, usually hex head. Used with nuts or in tapped holes.

Set Screws

Fully threaded, no head beyond the thread. Used to lock against other parts.

Wall Fixings

Solid Wall (Masonry)

• Wall plugs - Expand in hole when screw driven in. Match plug colour to screw size.
• Hammer fixings - Plug and screw combined, hammered in
• Sleeve anchors - Heavy-duty, expand when tightened
• Chemical anchors - Resin sets around a threaded rod. Very strong.

Plasterboard/Cavity Walls

• Spring toggles - Spring-loaded wings grip behind board. Very strong.
• Gravity toggles - Similar principle, different mechanism
• Self-drill fixings - Metal anchors that thread into board
• Hollow wall anchors - Metal sleeve that expands behind board

For heavy loads on plasterboard, find a stud or use multiple fixings.

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Materials and Finishes

Steel (Plain)

Indoor use only. Rusts when exposed to moisture.

Zinc Plated

Corrosion resistant. Good for damp indoor areas, not ideal for true outdoor use.

Stainless Steel

Excellent corrosion resistance. Use for outdoor, wet, or corrosive environments. More expensive.

Brass

Decorative, won't rust. Softer than steel - can damage if over-tightened.

Sizing

Screw Sizing (Gauge x Length)

Traditional gauge system (higher number = thicker) or metric diameter. Length is what enters the material, not total length.

Metric Threads

M6, M8, M10 etc. The number is the diameter in mm. Pitch (thread spacing) is standard unless specified.

Choosing the Right Fixing

Consider:

1. What materials are you joining?
2. What load will it bear?
3. Indoor or outdoor?
4. Need to be removable?
5. Aesthetic requirements?

When in doubt, go larger and stronger than you think necessary.

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