M4 M5 M6 Carriage Bolts with Hex Nuts – Zinc-Plated Steel, Full & Partial Thread

A general rule: the bolt length should equal the combined thickness of all materials being joined, plus enough thread engagement for the nut — typically 1.5× the bolt diameter. For example, joining two 15mm boards with M6 bolts, a 35mm (≈1-3/8") length is generally sufficient. Always add a washer if the material is soft wood or composite.

Load capacity depends on bolt diameter, length, material grade, and joint design. These zinc-plated steel bolts are generally rated for standard structural and woodworking loads. For safety-critical applications (e.g., load-bearing decks, playground equipment), consult a structural engineer and verify the grade marking on the bolt head.

The zinc plating provides moderate corrosion resistance suitable for covered outdoor use or occasional moisture exposure (e.g., a sheltered pergola or indoor workshop). For fully exposed outdoor installations, direct ground contact, or marine environments, stainless steel or hot-dip galvanized bolts are generally recommended.

Yes. These bolts follow the ISO metric coarse thread standard. M4 pitch is typically 0.7mm, M5 is 0.8mm, and M6 is 1.0mm. The included hex nuts are matched to the same standard, and the bolts are also compatible with standard metric washers, lock nuts, and wing nuts of the same diameter.

Full thread bolts are threaded along the entire shank, providing maximum grip in thinner materials and shorter lengths. Partial thread bolts have a smooth shank section near the head — the square neck locks into wood to prevent spinning, while the unthreaded shank provides a cleaner bearing surface in thicker assemblies. In this listing, M6 bolts 55mm and longer are partial thread; all M4 and M5 bolts are full thread.

Yes. Each pack includes matching zinc-plated hex nuts in the same quantity as the bolts. The nuts are pre-matched to the bolt thread size so no separate hardware purchase is needed for basic assembly. If you need washers, those are sold separately.

For typical deck rail or fence panel connections through 2× lumber (≈38mm / 1-1/2" actual thickness), M6 bolts in the 30mm–50mm range are commonly used. For heavier structural connections or post-to-beam joints through 4× or doubled lumber, longer partial-thread M6 variants (55mm–100mm) are generally more appropriate. Always verify fastener requirements with local building codes.