Wood screws: chipboard, double thread or stainless steel, which to choose?

The right wood screw depends on three things: length, drive and corrosion protection. The length must go into the second piece by at least two thirds; the Torx (TX) drive holds the bit better than the cross; zinc plating is enough for dry interiors, while outdoors you need A2 stainless steel. In the collection you will find diameters from 3 to 12 mm and lengths from 12 to 360 mm, with zinc-plated, black, yellow, bronzed, brass-plated or nickel-plated finishes.

The types

• Chipboard screws: for panels and furniture, with a thread that holds in wood-based materials.
• Double-thread screws: such as the Fischer STSR, for more demanding woodwork: see the data sheet for the intended use.
• ClassicFast and PowerFast quick fixing: Fischer series, for example the PowerFast FPF II CTF BC and the ClassicFast FCF II CTF BC, with A2 stainless steel versions such as the FPF II CTF A2.
• Wood screws with washer: for frames and battens, such as the CSC Edilizia ones.
• Self-tapping and Torx screws: in zinc-plated or stainless steel, for more general work.
• Assortments in a box: useful for those who do maintenance work and want to have several sizes within reach.

The collection includes many brands (Fischer, Unifix, Bossong, DeWalt, SPIT, Vigor, CSC Edilizia and A.M.E.S.) and a great many combinations of size, drive and finish. To get your bearings, start from the material to be fixed and the environment, then look for the length; the drive and the finish are chosen last.

How to choose by job

The features to look at

• Length (12-360 mm): at least two thirds of the screw must go into the second piece. Lengths over 100 mm are for beams and structures.
• Diameter (3-12 mm): roughly, small ones (3-4 mm) for finishing work, 5-6 mm for frames and battens, 8-12 mm for structures.
• Drive: PZ and PH are cross-head; TX (Torx) has a star-shaped recess that holds the bit better. Check that the bit is the right size (TX20, TX25, TX40).
• Head diameter: a wider head spreads the load better and does not sink into soft wood.
• Material and finish: white or yellow zinc-plated steel for interiors; A2 stainless steel for outdoors; bronzed, brass-plated or black for visible applications.
• Pack: from 10 to 1000 pieces.

A practical tip for those working on site: always keep two or three spare bits of the most-used size, because it is the worn bit, more than the screw, that causes the stripped head. And if you need to buy a large stock of a single size, choose the box of 1000 pieces and a Torx drive.

Common mistakes

• Screw too short: if it does not go two thirds into the second piece the fixing gives way.
• No pilot hole in hardwoods: the head cracks or the screw snaps, especially near the edges.
• Wrong bit: a PH1 on a PZ2 screw strips the head in a few turns.
• Zinc-plated screw outdoors: it stains and rusts. For anything that stays outdoors you need stainless steel.
• Too much torque: adjust the screwdriver's clutch and stop when the head is flush.

Frequently asked questions

Do I need a pilot hole?

In hardwoods and close to the edge, yes: it stops the wood from splitting.

Torx or cross-head: which is better?

Torx holds the bit better and reduces the risk of stripping the head, especially with a power screwdriver.

Zinc-plated or stainless steel?

Zinc-plated for dry interiors, A2 stainless steel for outdoors and damp environments.

What length should I use to join two planks?

Apply the two-thirds rule: if the first plank is 20 mm thick, the screw must be about 60 mm long, so that 40 mm goes into the second.

All the sizes are in the wood screws collection; to choose the right type or ask for a quote, write to the AMES technicians.