How to Select the Right Size of Connecting Bolts

A comprehensive guide on how to choose the right size of connecting bolts for your furniture. Learn about measuring, types, and sizes to ensure strong and reliable assembly. Your ultimate resource for furniture connecting bolts.

Understanding the Basics: What Are Connecting Bolts?

Walk into any modern home, and you will see beautiful, functional, and affordable furniture. Much of this is ready-to-assemble (RTA) or knock-down furniture. The secret to its sturdy construction lies in a small but mighty piece of hardware: the connecting bolt. Furniture connecting bolts, also known as connector bolts or joint connector bolts, are specialized furniture fasteners designed to join two pieces of wood or composite panels together. They are a cornerstone of the knock-down fittings system, which allows furniture to be shipped flat and assembled by the end-user. Unlike traditional wood screws, these bolts work with other hardware, like barrel nuts or cam lock fittings, to create a strong, secure, and often hidden joint. These clever fasteners are the unsung heroes of panel furniture. They make assembly easy and disassembly possible without damaging the furniture. This is why they are essential for manufacturers of cabinets, bookcases, beds, and desks. Using the right connecting bolts for furniture ensures a product that is not only easy to assemble but also durable and long-lasting.

Why Choosing the Right Size Matters

Selecting the correct size of connecting bolts is not just a technical detail; it is crucial for the safety, stability, and longevity of the furniture. A bolt that is too short will not create a secure joint, leading to wobbly and unsafe furniture. A bolt that is too long can protrude from the surface, creating a hazard and an unsightly appearance. It might even damage the wood panel by pushing through the other side.

The right size ensures:

• Maximum Strength: The bolt fully engages with its corresponding nut or fitting, creating a tight and robust connection that can withstand daily use.
• Structural Integrity: Correctly sized furniture hardware distributes stress evenly, preventing weak points that could lead to breakage.
• Flawless Aesthetics: The hardware fits perfectly, often concealed, contributing to a clean and professional finish.
• Efficient Assembly: Using the right components from the start saves time and frustration during the assembly process for both manufacturers and end-users.

For furniture manufacturers, standardizing on the correct connecting bolts sizes streamlines production and reduces errors. For importers and distributors, stocking the most common and effective sizes ensures you can meet the demands of your market.

Types of Connecting Bolts for Furniture

The world of furniture fasteners is diverse. While there are many variations, most connecting bolts for furniture fall into a few key categories, often used in conjunction with other fittings like dowel pins for alignment.

• Joint Connector Bolts (JCBs): These are the most common type. They have a machine thread and a flat, low-profile head (often with a hex or Allen key drive). They are used with barrel nuts or threaded inserts.
• Confirmat Screws: These are one-piece connectors with a coarse, deep thread that cuts directly into particle board or MDF. They provide a strong, rigid joint and are very popular in cabinet assembly.
• Cam Lock Connecting Bolts (Dowel Bolts): These bolts have a special head designed to be gripped by a cam lock fitting. This system allows for quick and easy assembly, creating a hidden joint that can be tightened with a simple turn of a screwdriver. This is a core part of the cam lock fittings system.
• Sex Bolts (or Barrel Bolts/Mating Connectors): This system consists of a male screw and a female "barrel" or post. They clamp material between them and are excellent for joining panels back-to-back, like in cabinet partitions.

Understanding these different types helps you select the right solution for your specific furniture design and material.

How to Measure Connecting Bolts Accurately

Knowing how to measure connecting bolts is a fundamental skill for any furniture professional. You need two key measurements: length and diameter.

Measuring the Length: The length of a connecting bolt is measured from the underside of the head to the tip of the bolt. It is not the total length including the head. This is critical. To determine the required length, add the thickness of the two panels you are joining, but make sure the bolt is slightly shorter than the total depth to ensure a tight fit without poking through. For example, if you are joining two 18mm panels (total 36mm), a 34mm or 35mm bolt would be appropriate, depending on the nut used.

Measuring the Diameter: The diameter refers to the thickness of the threaded part of the bolt. This is usually specified in metric units, like M6 (6mm) or M8 (8mm). You can measure this with a caliper for accuracy. The diameter determines the size of the pre-drilled hole and the strength of the connection. An M6 bolt requires a 6mm hole, and an M8 bolt needs an 8mm hole.

Always measure carefully. Precision here prevents costly mistakes in production and ensures a high-quality final product.

Connecting Bolts Sizes Chart

To simplify selection, here is a general furniture connecting bolts dimensions chart. This table provides common scenarios for panel furniture construction. Note that the required bolt length can vary slightly based on the specific type of nut or fitting used.

This connecting bolts sizes chart is a starting point. Always consider the material density and the stress the joint will endure when making your final selection.

M6 vs. M8 Connecting Bolts: What's the Difference?

A common question is whether to use an M6 or an M8 bolt. The choice between M6 connecting bolts vs M8 connecting bolts depends entirely on the application's load-bearing requirements.

M6 Connecting Bolts:

• Diameter: 6mm
• Common Use: The industry standard for most RTA furniture, including cabinets, bookcases, and light-duty desks.
• Advantages: Provides excellent clamping force for standard panel thicknesses (15-18mm). The smaller hole size is less intrusive on the panel's structure. It is cost-effective and widely available.

M8 Connecting Bolts:

• Diameter: 8mm
• Common Use: Reserved for heavy-duty applications where significant strength is needed. This includes bed frames, large tables, workbenches, and structural supports.
• Advantages: Offers superior shear strength and clamping force due to its larger diameter. It provides a more robust and durable connection for furniture that will endure high stress or weight.

For most cabinet assembly and general furniture, M6 is the perfect choice. When you are building something that needs to support significant weight or endure high physical stress, upgrading to M8 is a wise decision.

Selecting the Best Connecting Bolts for Particle Board and MDF

Particle board and Medium-Density Fiberboard (MDF) are the most common materials in panel furniture. They are cost-effective and versatile but require the right hardware to prevent damage.

For connecting bolts for particle board, the goal is to clamp the boards without crushing the wood fibers. Standard M6 JCBs with barrel nuts work exceptionally well. The barrel nut provides a large surface area for the bolt to pull against, distributing the load and preventing the bolt head from sinking into the relatively soft particle board. Similarly, for connecting bolts for MDF furniture, the same principles apply. MDF is denser than particle board, offering a better grip for threads. However, it can also split if the wrong fastener is used or if holes are not pre-drilled correctly. Confirmat screws are an excellent choice for MDF as their wide threads are specifically designed for this material, providing a very strong joint without a nut. When using standard bolts, ensure the pre-drilled holes are clean and correctly sized.

A Simple Connecting Bolts Installation Guide

This basic connecting bolts installation guide covers the use of a Joint Connector Bolt (JCB) with a barrel nut, a common combination in RTA furniture.

• Drill the Holes: First, align the two panels you want to join. Drill a hole through the face of one panel for the bolt to pass through. The hole diameter should match the bolt's diameter (e.g., 6mm for an M6 bolt).
• Drill the Cross-Hole: In the second panel, drill a larger hole in the edge that corresponds with the first hole. This hole must be wide enough to accept the barrel nut (e.g., 8-10mm).
• Insert the Barrel Nut: Drop the barrel nut into the cross-hole. Rotate the nut until its threaded hole lines up perfectly with the bolt hole. A small screwdriver can help with alignment.
• Insert and Tighten the Bolt: Push the connecting bolt through the first panel and into the barrel nut in the second panel. Use an Allen key or screwdriver to tighten the bolt. Do not overtighten, as this can damage the wood. Tighten until the joint is snug and secure. The two panels should pull together to form a tight, seamless joint.

Frequently Asked Questions (FAQ)

• Q: How do I choose connecting bolts for my project?

  A: Consider the total thickness of the panels you are joining and the weight the joint must support. Use our sizes chart as a guide and select a bolt that is slightly shorter than the total thickness. For heavy-duty applications, choose a larger diameter like M8.

• Q: What are the most common furniture connecting bolts sizes?

  A: The most common diameter is M6. Lengths vary widely, but common sizes for 15-18mm panels range from 28mm to 34mm.

• Q: Can I use connecting bolts for outdoor furniture?

  A: Yes, but you must use bolts made from corrosion-resistant materials like stainless steel or those with a specialized outdoor-grade coating to prevent rust.

• Q: What is the difference between a connecting bolt and a standard screw?

  A: Connecting bolts have machine threads and are designed to be used with a nut or a threaded insert, providing superior clamping force. Standard wood screws have tapered threads and cut directly into the wood, which can be less effective for repeated assembly and disassembly.

Partner with the Expert in Furniture Connecting Bolts

Choosing the right hardware is a critical step in furniture manufacturing. For a reliable supply of high-quality furniture connecting bolts and other knock-down fittings, partner with an expert. JINHAN is a leading manufacturer and exporter of furniture fasteners based in Dongguan, China. We offer a wide range of connecting bolts for furniture to meet your specific needs. Contact us for a quote at jasmine@gdjinh.com and secure your supply chain today.