What is the difference between screws, nails and bolts?
Which fastener suits which job, what the numbers on a screw box mean, and when a fixing needs a bolt rather than a screw.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 3 min
Short answer
Screws hold things together and can be undone; nails resist shear and are faster; bolts clamp two things with a nut and take real load. Choose by whether the joint needs to come apart, and by what the fastener is holding into.
A merchant's fixings aisle looks impenetrable and is mostly three decisions: what type, what size, and what coating. Get those right and the rest is detail.
Step by step
- Use screws for anything that may need undoing.The thread pulls the two pieces together and holds by friction along its whole length. It grips far better than a nail in withdrawal, and it comes out again.
- Use nails where speed and shear strength matter.Framing, fencing, floorboards, roofing battens. Nails resist sideways load well and are quick to drive, but they pull out easily and do not clamp.
- Use bolts where the load is real and the joint must not move.A bolt passes through both parts and clamps them with a nut and washer. Gates, structural timber connections, machinery. Unlike a screw, its strength does not depend on gripping wood fibres.
- Read screw sizes as gauge by length.A 4.0 x 50mm screw is 4mm across the thread and 50mm long. As a rule the screw should go at least twice as deep into the receiving piece as the thickness of the piece being fixed.
- Match the coating to the environment.Bright zinc indoors only. Outdoors use exterior-rated, hot-dip galvanised or stainless. Treated timber is corrosive to ordinary zinc — it needs stainless or a coating specifically rated for it.
- Pick the head for the job.Countersunk sits flush and is the default. Pan and flange heads sit proud and clamp thin material. Dome heads are decorative. Countersunk heads need a countersink or they split the surface.
- Choose the drive type deliberately.Pozidriv is the domestic standard. Torx grips far better and almost never cams out, which matters when driving long screws. Slotted heads exist for looks and are miserable to use.
- Use the right plug in masonry.A screw alone does nothing in brick. Match the plug size to the drill bit and screw gauge, drill deeper than the plug is long, and clear the dust out before inserting it.
- Pilot-drill hardwood and near edges.A pilot hole slightly narrower than the screw's core prevents splitting and lets the thread do its job. Essential in hardwood, near the end of a board, and always in the edge of MDF.
Tips
- Buy screws in a mixed box of sizes for general use and single sizes in bulk for a specific job. Running out halfway through a job with an unusual size is a real annoyance.
- Never mix stainless steel and galvanised fixings in wet locations — the contact between the two metals accelerates corrosion.
- Coach screws and coach bolts look similar. A coach screw threads into timber; a coach bolt goes right through and takes a nut.
Questions people ask
Should I use screws or nails?
Screws where you may need to undo it or where the fixing is pulled outwards; nails where you need speed and resistance to sideways load, such as framing and fencing.
What do the numbers on a box of screws mean?
Diameter across the thread in millimetres, then length in millimetres — so 4.0 x 50 is a 4mm screw 50mm long. Aim for at least twice the fixed piece's thickness in the receiving material.