Two Ways to Join Two Pieces of Metal

Walk into any UK workshop and you will find both a rivet gun and a tin of bolts within arm's reach. They solve the same basic problem — holding metal together — but they solve it in very different ways, and picking the wrong one costs you time, appearance or strength. Before you reach for either, ask yourself four questions: does this joint ever need to come apart, how much load will it carry, what does it need to look like, and what metals are you joining? The answers usually make the decision for you.

Rivets: Permanent, Fast and Light

Rivets form a permanent joint by deforming the tail of the fastener so it clamps the workpieces together. In most British workshops, that means blind (pop) rivets, available in 3.2mm, 4.0mm, 4.8mm and 6.4mm diameters in aluminium, steel and stainless steel. They are quick, they only need access to one side of the work, and they add very little weight or bulk. For trailer panels, ducting, signs, brackets and repair patches, they are hard to beat.

Two things trip people up. First, grip range: a rivet only clamps properly within a stated range of total material thickness, so measure your stack-up before ordering. Second, not all pop rivets are structural. Standard rivets are fine for sheeting and non-critical work, but load-bearing joints want structural rivets — sometimes called monobolts or interlock rivets — which have a locked mandrel and much higher shear strength. Where you need a flush finish, countersunk rivets sit nearly invisible in a countersunk hole, which is why they dominate aerospace and classic car work. Traditional solid rivets, set with a hammer or rivet gun against a buck, remain the neatest option for heritage and coachbuilding projects.

Bolts: Strength You Can Take Apart

Bolts are the disassembly champions. A bolted joint can be tightened, adjusted, inspected and replaced with hand tools, which matters enormously on anything that moves, wears or needs maintaining — machinery guards, hinges, tow bars, racking, engine mounts.

They are also far stronger than most people assume, provided the joint is designed properly. A grade 8.8 steel bolt is the everyday workhorse, with 10.9 for higher loads and A2 or A4 stainless for corrosion resistance. Strength does not come from the bolt alone, though; it comes from preload. Torque the bolt correctly and the clamped parts are held together by friction, so the fastener sees far less shear than a loose one would. That means clean, dry threads or a light oil as specified, hardened washers under the head and nut, and the right thread engagement — roughly 1.5 times the bolt diameter in steel and twice the diameter in aluminium or castings.

Anything subject to vibration needs a locking strategy: nyloc nuts, a threadlocker, or a properly applied torque figure checked at intervals.

Strength, Appearance and Disassembly Compared

• Strength: A well-preloaded bolted joint generally beats a riveted one in shear and tension, especially in thicker material. Structural rivets close the gap and are excellent in thin sheet where bolts would distort or need a washer on both faces.
• Appearance: Rivets sit flush or nearly flush and give a clean, uniform line. Bolt heads and nuts protrude, though button, countersunk and socket heads can tidy this up considerably.
• Disassembly: Bolts undo. Rivets must be drilled out, which risks enlarging the hole and damaging paint — plan for a slightly larger replacement rivet if you expect to dismantle the joint.
• Speed and access: Rivets win outright. A blind rivet needs one side only and takes seconds; a bolt needs two-sided access, a spanner, a socket and a torque figure.
• Weight and thickness: Rivets suit thin sheet and weight-sensitive work. Bolts suit thicker sections, tapped holes and anything needing a defined clamp load.

The Materials Question: Corrosion and Dissimilar Metals

British weather is unforgiving, so corrosion decides as much as strength does. Zinc-plated bolts are fine indoors and in dry workshops; for outdoor, coastal or washdown environments, move to A4 stainless or hot-dip galvanised fixings. Aluminium rivets are ideal for aluminium sheet because they avoid galvanic trouble, but they are soft — use stainless or monel rivets where load matters, accepting the small galvanic risk and managing it.

Whenever you join dissimilar metals — stainless bolts into aluminium brackets, steel fasteners into a stainless panel — you create a small battery that eats the softer metal whenever water is present. Break the electrical path with nylon isolating washers, a bedding compound or a strip of plastic tape between the faces, and always deburr holes so coatings stay intact. Never mix fixings casually on a job that lives outdoors.

Choosing Well in the Workshop

A simple rule works for most jobs: if it must come apart or carry serious load, bolt it; if it is a permanent skin, panel or patch, rivet it. Where both seem to fit, think about maintenance. A riveted cover on a gearbox might save ten minutes today and cost an hour when the seal fails.

Whichever you choose, preparation decides the result. Drill to the nominal diameter rather than oversize, deburr both faces, clamp or cleco the parts so the holes align before you fasten anything, and check that hole centres sit at least two diameters from an edge. Mark bolt heads with a paint stripe after torquing so a later glance tells you nothing has moved. Do that, and both rivets and bolts will serve you well for years — the trick is simply knowing which one the job is asking for.