Furniture Screws & Wood Screws — PH, PZ, TX

Furniture screws and wood screws are fixings with an asymmetrical thread profile that cuts form-fittingly into engineered timber materials such as chipboard, MDF, or solid wood when driven in.

Furniture making requires a high degree of precision. Whether building a cabinet carcase, mounting fittings, or securing a back panel – selecting the correct screw determines the stability and durability of the finished piece. The wrong drive, an unsuitable diameter, or the incorrect thread type can result in stripped fixings, split wood, or damaged screw heads. This guide provides the necessary technical background knowledge on drives, dimensions, and the proper use of fastening materials in professional furniture making.

The Anatomy of a Furniture Screw

Before examining specific drive types, the basic components of a screw must be defined. Every screw for furniture construction consists of three primary segments, whose specific design determines the exact area of application.

The Screw Head

The head serves to transmit torque from the tool to the screw and forms the visible termination of the joint.

• Countersunk Head: The most frequently used head shape in woodworking. The head tapers downwards (usually at an angle of 90°) and sits flush with the timber surface. This is essential whenever components must lie flat against one another.
• Pan Head (Round Head): This head sits flat on top of the material surface. It is primarily used for securing metal fittings to wood, for instance when installing guide rails for a full-extension runner, where a countersunk head would distort the thin sheet metal.

The Thread: Full Thread vs. Partial Thread

• Full Thread: The thread extends from the point right up to beneath the screw head. It provides exceptionally high pull-out values and is used to secure fittings onto wood.
• Partial Thread: The thread covers only the lower section of the shank, whilst the upper area remains smooth. This geometry enables two wooden components to be pulled tightly together. The thread grips in the bottom component while the smooth shank rotates freely in the top component, drawing the upper piece firmly against the lower one.

The Point

Classic wood screws require a tapered point to displace the material as they are driven in. Modern chipboard screws often feature a cutting notch or self-drilling tip. This reduces splitting in the wood and lowers the torque required during insertion.

Screw Drive Comparison: PH, PZ, and TX

The drive recess in the screw head is the interface with the tool. Selecting the correct driver bit is critical. An incorrect bit in a screw head acts like the wrong key in a lock cylinder – it spins out, fails to transfer torque, and, in the worst case, strips the profile. Three systems dominate furniture making.

Cross Recess PH (Phillips)

The Phillips drive is the classic cross-slot design. It is characterised by flanks that taper downwards (wedge-shaped). This design was originally developed to cause the tool to slip out of the screw automatically under excessive torque (the so-called cam-out effect). Whilst this prevented overtightening in early industrial assembly lines, today it requires the user to exert significant axial downward pressure to prevent the bit from slipping.

In furniture assembly, this drive is often found on pre-fitted components or smaller fixings. When sourcing replacements or planning specific installations, wood screws PH1 are used for smaller diameters and wood screws PH2 for standard applications.

Cross Recess PZ (Pozidriv)

The Pozidriv drive is a direct evolution of the Phillips system. It can be identified by four additional fine radial ribs between the main cross slots. The decisive technical difference lies in the flanks: on a PZ drive, they run parallel rather than tapered.

This drastically reduces the cam-out effect. The bit seats much more securely in the screw head, requires less downward pressure, and allows higher torque transmission. For assembling cabinet carcases made from chipboard, this drive is widely utilised. Depending on the screw size, wood screws PZ1 (for delicate work) or wood screws PZ2 (the standard in furniture construction) are deployed.

Torx TX (Star Drive)

The TX drive (often known by the brand name Torx) features a star-shaped, wave-like profile with six lobes. It offers the most efficient torque transmission of all common drives. Because the driving force acts perpendicular to the contact flanks, there are virtually no cam-out forces. The bit does not slip, and wear on both the tool and screw is minimal. In professional joinery and high-end furniture, the TX drive is increasingly replacing cross-recess alternatives because it allows fatigue-free working.

Diameters and Lengths: Reading Dimensions Correctly

Screw dimensions are always specified in mm. The notation follows the format: thread diameter x total length. A screw designated `4.0 x 40 mm` therefore has an outer thread diameter of 4 mm and a total length of 40 mm. For countersunk screws, the length is measured including the head, whereas for pan-head screws, only the shank length beneath the head is measured.

The choice of diameter depends on material thickness and expected mechanical loads:

• 3.0 mm: Ideal for delicate work, thin back panels made of HDF, or small fittings. Matching wood screws 3mm prevent thin mouldings and battens from splitting.
• 3.5 mm: The standard dimension for many furniture fittings. In particular, mounting plates for concealed hinges or lightweight drawer runners are frequently fixed into cabinet side walls using wood screws 3.5mm.
• 4.0 mm: The versatile all-rounder for carcase construction. Wood screws 4mm offer ample pull-out strength to reliably join shelves, side panels, or heavier hardware.
• 5.0 mm and larger: Used for structural load-bearing assemblies, heavy furniture legs, or mounting wall-hung base units and cabinets.

Material and Finish: Zinc, Black, and Stainless Steel

In addition to mechanical geometry, the alloy and surface finish of a screw play a key role in aesthetics and corrosion protection.

• Bright Zinc Plated (BZP) Steel: The absolute standard for indoor use. A thin layer of zinc shields the steel against ambient humidity. Zinc wood screws are cost-effective and blend neutrally with light wood finishes or standard metal hardware.
• Black Oxide / Black Zinc Plated: In line with modern interior trends featuring matt black hardware, dark wood finishes, or industrial aesthetics, black wood screws are increasingly favoured. They eliminate distracting silver reflections against dark hinges or handles.
• Stainless Steel (A2 / A4): Essential for furniture in high-moisture environments (such as bathrooms), outdoor applications, or when working with timber high in tannic acid (such as oak). Standard steel screws would corrode in these settings or react with tannins to cause dark discolouration in the wood.

Specialist Furniture Screws and Connectors

While classic wood screws and furniture screws cut their own mating thread, professional furniture making relies on additional standardised connectors.

Euro Screws

These screws feature a flat underside, a thicker shank (typically 6.3 mm), and a very coarse thread profile. They are designed specifically for System 32 drilling patterns. This means they are inserted directly into pre-drilled holes measuring exactly 5 mm in diameter. Euro screws provide significantly higher pull-out resistance in porous materials like chipboard compared to standard wood screws and are the benchmark for fixing drawer runners, cruciform mounting plates, and shelf supports.

Cam and Dowel Connectors (Minifix / Cam Locks)

These two-part fittings consist of a threaded steel dowel (bolt) and a circular cam housing. They allow furniture panels to be joined securely and dismantled without causing damage. The dowel is screwed into a pre-drilled hole, whilst the cam casing is inserted into a drilled recess (usually 15 mm). Turning the cam by approximately 180° pulls the dowel head inward, clamping the components firmly together.

Threaded Inserts (Rampa Inserts)

When an engineered panel or softwood requires a strong metric thread (e.g., M6 or M8) – such as for fitting height-adjustable furniture feet – threaded inserts are used. They feature a coarse external wood thread and a female metric machine thread on the inside.

Step-by-Step: Driving Screws into Wood (Without Splitting)

Correct installation technique is just as crucial as the hardware itself. Particularly near edges or in end grain, timber materials are prone to splitting if a screw is driven in without proper preparation.

Tools Required

• Cordless drill/driver with adjustable torque clutch
• Matching bits (PH, PZ, or TX) correctly sized to the screw head
• Wood drill bits (with centring brad point)
• Countersink bit
• Rule or vernier calliper

Installation Guide

1. Check the Bit: Seat the driver bit into the screw head by hand. It must fit snugly without play or wobbling.
2. Pre-drilling (when necessary): Pre-drilling is always mandatory in hardwoods and MDF. In softwoods or chipboard, pre-drilling is strongly advised near edges. The drill bit diameter should match the core diameter of the screw (outer thread diameter minus thread depth). Rule of thumb: for a 4 mm screw, pre-drill with a 2.5 mm or 3 mm bit.
3. Countersinking: If using a countersunk screw that needs to sit flush, prepare the hole using a countersink bit. This prevents the surface veneer or grain from tearing as the head is driven in.
4. Set the Torque: Set the adjustable clutch of your cordless driver to a lower torque setting. When the screw head reaches flush alignment, the clutch should disengage (slip) to avoid stripping the wood.
5. Drive the Screw: Position the screw straight. When using PH or PZ drives, apply firm axial downward pressure. Drive the screw at medium speed until the head sits perfectly flush.

Frequently Asked Questions (FAQ)

Do I always need to pre-drill into chipboard?

No, not always. Modern chipboard screws equipped with cutting notches or milling ribs can often be driven directly into board surfaces without pre-drilling. However, when working close to edges (less than 3 cm from the edge) or screwing directly into the narrow end grain of chipboard, pre-drilling is essential to prevent the wedging action of the screw from splitting the core.

What is the difference between PH and PZ?

The PH drive (Phillips) features tapered flanks that tend to push the tool outward under high resistance. The PZ drive (Pozidriv) features parallel flanks and additional radial ribs. It provides superior grip for the bit and can transmit higher torque without slipping. The two systems are not interchangeable – using a PZ bit in a PH screw will damage the recess.

When should I use a full thread versus a partial thread?

A full thread is used when securing metal or plastic hardware (such as hinges or runners) onto timber, ensuring maximum thread engagement along the entire screw length. A partial thread is used to clamp two timber components together, as the unthreaded upper shank spins freely in the top piece while the lower thread pulls it tight.

Which screws should I use for concealed cabinet hinges?

Concealed cup hinges are generally secured in one of two ways. If the cabinet uses the standardised hole grid (System 32), Euro screws are driven into 5 mm pre-drilled holes. Without a pre-drilled system grid, countersunk screws measuring 3.5 mm in diameter and 15 mm or 17 mm in length are standard, ensuring they do not pierce through a typical 16 mm or 18 mm cabinet carcase wall.

How can I fix a stripped screw hole?

When a screw spins freely in timber (meaning the internal thread in the hole is stripped), it loses all holding strength. To rectify this: back the screw out completely. Add a small amount of wood glue and insert one or two wooden matchsticks (without heads) or toothpicks into the hole. After drying briefly, drive the original screw back in. Alternatively, replace it with a screw of a larger diameter (e.g., 4.5 mm instead of 4.0 mm).

Why does timber split when driving screws?

Wood splits when the solid volume of the inserted screw displaces the wood fibres beyond their tensile limit. This happens frequently in dense hardwoods, overly dry boards, or when screwing parallel to the grain into end grain. Pre-drilling a pilot hole matching the screw core diameter reliably prevents splitting.

Which bit fits which screw?

Screw packaging clearly indicates the required drive type and size (e.g., TX20, PZ2, PH1). The bit must match exactly. Using an undersized bit (such as a PZ1 bit in a PZ2 screw) leads to immediate slippage and strips the recess.

Related Categories & Guides

To find the ideal fixings for your next joinery or cabinet project, explore our specialised categories for furniture hardware. Always ensure you match thread, head geometry, and drive type for optimal assembly performance.

• Overview of all wood screws and furniture screws
• Wood screws with Pozidriv cross recess PZ1
• Wood screws with Pozidriv cross recess PZ2
• Wood screws with Phillips cross recess PH1
• Wood screws with Phillips cross recess PH2
• Wood screws 3 mm diameter
• Wood screws 3.5 mm diameter
• Wood screws 4 mm diameter
• Black wood screws for dark hardware designs
• Bright zinc-plated wood screws for standard applications