Wood Screws in Furniture Making: PZ, TX and Chipboard Screws Explained

The term Spax has established itself as a generic term for modern chipboard screws and wood screws. These are self-tapping screws with an asymmetrical thread, used in furniture making to create durable joints in engineered wood materials. Common screw drive types are Pozidriv (PZ) and Torx (TX), with typical nominal diameters ranging between 3 mm and 5 mm.

What Exactly Are Wood Screws and Chipboard Screws?

Whilst traditional wood screws often feature a tapered core and usually require pre-drilling, modern chipboard screws (frequently referred to colloquially as Spax) are optimised for efficient use in engineered wood materials such as chipboard, MDF, or multiplex plywood.

The asymmetrical thread anchors directly into the panel material like a barb, preventing pull-out under tensile loads. The sharp thread point often allows pinpoint placement without pre-drilling, although pre-drilling remains good professional practice in hard materials or near edges to prevent the wood from splitting. A distinction is also made between fully threaded screws (for high pull-out resistance) and partially threaded screws (for clamping two components tightly together).

Drive Types: PZ, PH and TX Compared

Choosing the correct drive type is crucial for power transmission and preventing tool wear (cam-out effect).

• Pozidriv (PZ): The standard in furniture making. In contrast to a simple Phillips drive, the flanks here run parallel, which significantly reduces bit slippage. PZ1 wood screws are often used for delicate fitting installations, whilst PZ2 wood screws are mostly chosen for cabinet carcass joints.
• Phillips (PH): The classic cross-head with tapered flanks. It tends to push the bit out of the screw head under high torque. In professional cabinet making, it has largely been superseded by PZ and TX.
• Torx / Star Drive (TX): Offers the highest torque transmission without downward pressure. The star-shaped profile completely prevents bit slippage and is the preferred choice, particularly for longer screws or hard timber.

Typical Dimensions and Standards in Furniture Making

When fitting furniture hardware such as concealed cup hinges or drawer runners, exact dimensions must be maintained to avoid obstructing the mechanism or piercing through the mounting panel.

• Diameter: For fixing standard hinges and runners (System 32), 3.5mm wood screws or 4mm wood screws are the norm. For more delicate components, 3 mm is also used.
• Length: Screw length depends on material thickness. With an industry-standard chipboard thickness of 18 mm, the screw must be a maximum of 15 mm - 16 mm long for single-sided mounting. For 16 mm thick panels, fitters select appropriately shorter options (e.g. 13 mm - 14 mm).

Variations: Head Shapes and Aesthetic Adaptation

In addition to technical performance, appearance plays a role in visible screw fixings. The head shape must also match the respective hardware fitting.

• Countersunk Head: Sits flush with the material surface. Most furniture fittings have corresponding countersinks in their mounting holes.
• Pan Head / Raised Head: Sits flat on top of the material. Used when the component lacks a countersink (e.g. with thin metal brackets) or when clamping force needs to be distributed over a wider area.
• Colours and Covers: To match the decor, screws with colour-coated heads are available. Black wood screws are used on dark industrial-style furniture or matt black fittings, while white screws suit light cabinet interiors. Alternatively, plastic cover caps are pushed directly onto the screw head (usually PZ2 or TX20).

Application & Selection

The correct selection of wood screws and furniture fixings defines the overall stability of the furniture unit. For hidden, highly stressed carcass joints, joiners often rely on specialised direct-drive connecting screws (Confirmat) or two-part furniture connectors such as cam and dowel connectors.

When mounting fittings such as hinge mounting plates, ensuring the correct diameter is essential, as oversized screw heads can obstruct the clip-on mechanism of the hinge.

Related Terms

• Euro Screw: A specialised blunt-ended fixing screw with a 5 mm diameter, precisely matched to the pre-drilled hole pattern in System 32.
• Threaded Insert (Rampa Bushing): A threaded insert that is screwed into wood to provide a metric internal thread (e.g. M4 or M6) for machine screws.
• Cam-out Effect: The unintended slipping of the screwdriver bit out of the screw head as torque increases (especially common with PH drives).