Connecting Bolts 8mm to 34mm: Choosing the Correct Length for Strong Cabinet Joints

April 16, 2026

A short connecting bolt with an 8 mm to 24 mm thread length is suitable for thin panel materials and light connections, whereas lengths from 28 mm to 34 mm are designed for high pull-out forces in thick substrate panels or solid wood.

The stability of any piece of furniture stands and falls with the quality of its fittings. In modern furniture construction and professional joinery assembly, connecting bolts combined with a cam lock fitting are the gold standard. Together they form a strong, force-locking joint that remains fully demountable at any time. Yet, not every steel pin is identical. Choosing the exact length – from very short 8 mm versions right up to long 34 mm models – determines whether a joint breaks, tears out under load, or holds permanently.

This technical comparison examines the mechanical differences between various lengths and demonstrates which dimensions are strictly required for standard-compliant carcase construction.

The Mechanics Behind Connecting Bolts

A connecting bolt functions as a tie rod. It is screwed into the edge or face of a substrate panel (usually chipboard or MDF). The protruding end with the spherical head engages with the pre-drilled hole of the mating panel, where it is gripped and pulled tight by a cam.

The critical area is the thread seated within the wood-based material. Pull-out strength, measured in Newtons (N), depends directly on the thread flank engagement in the substrate. The more porous the core of the panel (as found in standard chipboard), the more thread turns must bite to distribute the force across a larger surface area.

Short Connecting Bolts (8 mm to 24 mm)

Short bolts are designed for standard light-to-medium furniture construction tasks as well as specialised construction nodes.

The 8 mm Connecting Bolt: Specialist for Centre Partitions

An 8mm connecting bolt features an extremely short thread. Typically, this is not a self-tapping wood thread, but a metric M6 thread. This variant is used almost exclusively in conjunction with an insert nut (threaded sleeve) or a through-hole in centre divider panels. When two shelves need to be mounted at the exact same height to the left and right of a centre partition (twin assembly), the space inside a 16 mm or 19 mm board is insufficient for two deep wood threads. In this scenario, an insert nut is fitted into the centre panel, into which an 8 mm bolt with an M6 thread is screwed from each side.

The 24 mm Connecting Bolt: The Industry Standard

The 24mm connecting bolt is the classic all-rounder for panel thicknesses of 15 mm and 16 mm. It features a so-called Euro thread (a specialised coarse-pitch thread) that cuts directly into a 5 mm pilot hole. With a 16 mm thick panel, a drilling depth of approximately 12 mm to 14 mm provides adequate hold without breaking through the decorative surface on the opposite side.

Long Connecting Bolts (28 mm to 34 mm)

As panel thickness increases or heavier loads must be borne, short threads reach their physical limits. This is where longer versions come into play.

The 28 mm Connecting Bolt: For Solid Carcase Construction

For high-quality furniture built from 19 mm or 22 mm thick panels, the 28mm connecting bolt is the professional choice. The longer thread makes full use of the extra panel thickness. More thread turns in the wood translate into greater resistance against shear forces and tensile stress. This is particularly relevant for wide construction shelves in wardrobes or heavy sideboards.

The 34 mm Connecting Bolt: Maximum Load Absorption

The 34mm connecting bolt is designed for heavy-duty applications, solid timber, and thick panels from 22 mm upwards. Acting like a deep bridge pier, the long thread anchors itself deep into the core of the panel and distributes tensile loads across a maximum area. This length is frequently used when high structural requirements apply, such as wall-hung units, platforms, or when using softer substrates (like certain blockboards) where a short thread might tear out under load.

Technical Differences in Direct Comparison

Selecting the right length is not a matter of aesthetics, but purely of statics and dimensional tolerances.

Thread type and pilot drilling: Lengths of 24 mm, 28 mm, and 34 mm usually feature a Euro thread for a 5 mm hole in the System 32 grid. The 8 mm variant requires an M6 female thread in the mating component.
Minimum panel thickness: A 34 mm bolt requires a drilling depth of at least 15 mm to 17 mm into the wood. Therefore, it cannot be screwed into a 16 mm panel without breaking through the decorative veneer on the back. A 24 mm bolt must be used here instead.
Pull-out resistance: In identical panel materials (e.g. 19 mm chipboard), the 28 mm bolt offers measurably higher pull-out resistance than the 24 mm bolt, as it penetrates deeper into the denser outer layers of the chipboard.
Visible clamping distance: Regardless of the thread length concealed within the wood, the clamping dimension (the distance from the collar of the bolt to the spherical head) must match the used cam lock fitting precisely. Standard drilling distances are typically 24 mm or 34 mm from the panel edge to the centre of the cam hole.

Decision Guide: Which Length for Which Project?

Planning furniture carcase connector systems requires exact coordination with the board material.

Choose 8 mm (M6 thread):

For back-to-back twin connections on a shared centre partition (combined with an insert sleeve).
When the bolt is screwed into metal inserts or threaded plates.

Choose 24 mm (Euro thread):

For standard furniture making using 15 mm or 16 mm thick boards.
For light carcases, drawer back panels, or small shelving units.

Choose 28 mm (Euro thread):

For premium furniture builds using 18 mm or 19 mm material thicknesses.
For larger wardrobes and robust office furniture.

Choose 34 mm (Euro thread):

For panel thicknesses from 22 mm.
For heavily loaded joints, bed frames, or solid wood constructions.
When the drilling distance of the cam sits deep within the mating panel to achieve higher edge strength around the hole.

Material and Drive Types

Connecting bolts for professional use are manufactured from hardened steel or solid die-cast zinc. While some hardware fittings utilise plastic housings for the cam, the bolt itself is always made of metal as a load-bearing component.

For assembly, bolts usually feature a cross-recess (PZ2) or a Torx drive (TX20). A clean drive profile is crucial, as screwing into un-drilled or tightly pre-drilled MDF demands high torque. The bolt must be inserted perfectly square and driven right up to the collar. If it sits crooked or not deep enough, the cam cannot grip the head correctly, leading to open gaps in the carcase joint.

Frequently Asked Questions (FAQ)

Can I screw a 34 mm bolt into a 16 mm thick chipboard? No. The threaded section entering the wood is too long on the 34 mm version. The pilot hole would need to be deeper than the panel thickness, causing the drill or screw tip to punch through the decorative face. For 16 mm boards, the 24 mm variant is strictly required.

What is the difference between a Euro thread and a metric thread on connecting bolts? A Euro thread is self-tapping and screws directly into a 5 mm pilot hole in wood-based materials. A metric thread (such as M6 on short bolts) requires a matching internal thread in the workpiece, typically provided by an inserted metal nut.

Can joints made with connecting bolts and cams be dismantled? Yes, these systems are classic demountable cabinet connectors. Turning the cam half a turn anti-clockwise releases the head of the bolt. The furniture unit can be taken apart and reassembled as often as needed without losing structural stability.

What drill bit diameter is required for a Euro thread? The industry standard pilot hole diameter for Euro-thread connecting bolts is 5 mm. The hole must be drilled at an exact 90° angle, ideally using a pillar drill or within the standard 32 mm system grid to ensure the bolt sits flush and straight.