Selecting and Fitting Table Legs by Thread Size: M8 vs M10

Table legs and furniture feet with a metric thread are anchored into furniture components using a threaded insert or a prong tee nut, with M8 and M10 thread sizes defining standard load capacities and stability levels.

Choosing the correct fixing method is crucial for the overall stability of tables, cabinets, and chests of drawers. A metric thread provides the major benefit of allowing connections to be dismantled and reassembled at any time without causing damage. This guide is aimed at fitters, joiners, and ambitious DIY enthusiasts planning a technically sound installation of screw-in legs and feet.

The Technical Basics: M8 vs M10

Metric ISO standard threads are standard practice in furniture construction. The designations state the nominal outer diameter of the thread.

• M8: Features a nominal diameter of 8 mm and a thread pitch of 1.25 mm. This size is the industry standard for most furniture feet, sofa legs, cabinet feet, and lighter table legs. Its tensile strength is entirely sufficient for static loads in standard domestic environments.
• M10: Features a nominal diameter of 10 mm and a thread pitch of 1.5 mm. The larger cross-section significantly increases bending stiffness and shear force resistance. M10 is used on heavy dining tables, workbenches, or solid oak tops where substantial leverage forces act upon the fixing point.

Deciding between these two sizes primarily depends on the length of the leg and the overall weight of the furniture piece. A 710 mm long table leg generates considerably more torque at the mounting point under lateral loads than a 100 mm high cabinet foot, due to leverage.

Types of Table Legs and Furniture Feet with Threaded Connections

A broad selection of support components with integrated threaded studs is available. The design dictates the intended application.

1. Height-Adjustable Table Legs

Floors are rarely perfectly level. Height-adjustable table legs feature an integrated mechanism in the foot glide, typically offering height regulation of 10 mm - 30 mm via an internal thread. This prevents table wobble on uneven tiles or floorboards.

2. Metal and Steel Legs

For modern interior layouts and high structural demands, metal table legs are the standard choice. Here, the threaded studs are welded or pressed directly into the top mounting plate. Finishes such as white table legs integrate subtly into bright spaces, whilst powder-coated steel provides an industrial look.

3. Adjustable Furniture Feet for Carcase Furniture

Heavy wardrobes or fitted kitchen units rely on adjustable furniture feet. These are frequently equipped with an M8 thread and are screwed straight into the underside of the carcase. Options such as square furniture feet or cylindrical designs provide different surface contact areas to distribute the load. Chrome furniture feet offer a decorative finish in living and bathroom spaces.

Matching Female Connectors: Threaded Inserts and Sockets

A metric thread cannot be driven straight into timber. It requires a matching connector anchored within the wood to supply the internal metric thread. Three primary categories exist:

Screw-in Threaded Inserts (Insert Nuts)

The screw-in threaded insert is the most refined technical solution for blind holes in thick table tops. The insert features a coarse, self-tapping external wood thread and a metric internal thread (e.g. M8 or M10). It is driven into a pre-drilled hole. Advantage: High pull-out resistance, as the external thread cuts deeply into the wood grain.

Prong Tee Nuts

This design features a flat flange with retaining prongs and a barrel containing the internal metric thread. It is driven from the reverse side (opposite the direction of the load) into a through-hole. When the leg is tightened, the prongs bite into the timber. Disadvantage: Requires a hole drilled all the way through the material, which is not suitable for an exposed table surface. It is best suited for hidden structures, such as upholstered frames or the base of cabinet carcases.

Threaded Mounting Plates

If the material thickness of the top is insufficient for an insert (e.g. 16 mm chipboard), surface-mounted threaded plates are used. These metal plates feature a central threaded socket (M8/M10) and are secured to the surface using three or four standard chipboard screws (typically 4 x 15 mm).

Selection Criteria: Choosing the Right System

The combination of leg, thread size, and insert must be tailored to the specific project. Consider the following factors:

1. Material Thickness of the Base Panel

A threaded insert requires adequate material depth. An M8 insert is typically 15 mm - 20 mm long. The drilled hole must be 2 mm - 3 mm deeper than the insert itself. Therefore, the table top should be at least 22 mm - 25 mm thick to avoid breaking through the surface. For thinner panels, mounting plates should be used instead.

2. Material Properties (Timber Species)

Solid wood (oak, beech) behaves differently from MDF or chipboard when driving in threaded inserts. In hardwood, the pilot hole diameter must be exact (often 0.5 mm - 1.0 mm larger than in softwood), because the dense material will not give, which could cause the insert to jam or the timber to split.

3. Static Load and Leverage Forces

The longer the leg, the greater the leverage acting on the threaded connection. For bedside tables, where legs are often only 150 mm - 200 mm high, an M8 thread in a standard insert is completely adequate. For a freestanding dining table with 720 mm legs, M10 or heavy-duty mounting plates should be selected to withstand lateral forces when the table is bumped.

Installation Guide: Fitting Table Legs and Threaded Inserts Correctly

Anchoring the insert into the timber serves as the foundation of the assembly – if this fails, even the strongest steel leg is useless. Drilling precision is essential.

Required Tools

• Cordless drill/driver or power drill
• Lip-and-spur wood drill bit (diameter matched to the insert's core body)
• Depth stop or masking tape to mark the drilling depth
• Hex key (Allen key) to drive the insert
• Countersink bit (optional)

Step 1: Pilot Drilling

Determine the core diameter of the screw-in insert (excluding the outer thread ridges). This dimension corresponds to the required drill bit diameter. For an M8 insert with a 14 mm outer diameter, drill at 12 mm in softwood, or 12.5 mm - 13 mm in hardwood. Always use a drill bit with a centring point to prevent wandering. Set the depth stop so that the hole is 2 mm deeper than the insert length.

Step 2: Countersink the Edge (Optional but Recommended)

Lightly countersink the rim of the drilled hole (approx. 1 mm - 2 mm). This prevents the top wood fibres from tearing or swelling upwards when the insert is driven in, ensuring the table leg sits perfectly flush against the wood.

Step 3: Driving in the Threaded Insert

Use the correct hex key for the internal socket of the insert. Drive the insert into the wood at an exact 90° angle. Apply firm, even downward pressure. The insert must sit completely flush or slightly (0.5 mm) below the wood surface. If it protrudes, the leg will not sit flat against the panel, causing instability.

Step 4: Fitting the Table Leg

Screw the threaded stud of the table leg into the metric internal thread by hand. Rotate the leg until it sits firmly against the mounting panel. Overtightening with tools is unnecessary and may damage the thread.

Avoiding Common Installation Mistakes

1. Drilling off-angle: If the blind hole is not drilled at an exact 90° angle, the insert will sit crookedly. Consequently, the screwed-in leg will also be out of alignment. Using a drill guide helps prevent this.
2. Pilot hole too small: If the hole in hardwood is drilled too narrow, driving the insert requires excessive torque. This frequently leads to the socket stripping or the wood splitting.
3. Pilot hole too large: The external thread will fail to bite, stripping out and losing all tensile hold. In this scenario, setting the insert in place with epoxy resin is often the only remedy.

FAQ – Frequently Asked Questions About Thread Sizes and Table Legs

Which thread size is better for a dining table: M8 or M10?

For a full-sized dining table with tall legs (approx. 710 mm - 730 mm) and a heavy solid wood top, M10 is the more reliable technical choice. The greater bending resistance of a 10 mm stud handles horizontal knocks far better than an M8 thread.

How deep does the hole for a threaded insert need to be?

The blind hole must always be drilled 2 mm - 3 mm deeper than the total length of the screw-in insert. This ensures the insert can be fully seated below the surface without bottoming out.

Can I screw an M8 leg into an M10 thread?

No, the diameter and thread pitch are completely incompatible. An 8 mm stud will simply drop through a 10 mm female thread. Thread reducer adapters (M10 male to M8 female) exist, but they add height and create a gap between the leg and the table top.

What drill bit size is needed for an M8 insert nut?

This depends on the specific insert's external body diameter and the timber species. A typical M8 insert has a 14 mm outer thread diameter. Softwoods (pine, spruce) are generally drilled at 12 mm, whereas hardwoods (oak, beech) require 12.5 mm or 13 mm. Always consult the manufacturer's technical specifications.

What should I do if a threaded insert pulls out of the timber?

If the insert has stripped its hole, the hole can be enlarged to the next size up (e.g. from 12 mm to 15 mm) to fit a larger insert with the same internal M8 thread. Alternatively, the damaged hole can be plugged with a glued hardwood dowel, allowed to cure, and re-drilled.

Are threaded table legs always height-adjustable?

Not necessarily. The top thread (M8/M10) is designed purely for fastening the leg to the underside of the surface. Height adjustability depends entirely on the foot glide at the bottom. Many metal and wooden legs feature an additional threaded insert at the base to accommodate an adjustable levelling foot for uneven surfaces.

Can I use threaded inserts in chipboard?

Yes, though pull-out strength in chipboard is lower than in solid wood. Use longer inserts with a coarse, deep external thread to grip as much core material as possible. For heavily loaded connections in chipboard, surface mounting plates with multiple screw fixings often provide superior stability.

Related Categories & Hardware Guides

• Table legs – Overview of designs, materials, and mounting styles.
• Threaded inserts – Sockets, prong tee nuts, and mounting plates for metric threads.
• Furniture feet – Support feet for sideboards, sofas, and carcase furniture.
• Height-adjustable table legs – Level regulation solutions for uneven floors.
• Metal table legs – Robust designs for modern interior schemes.