Two bolts can look identical on the shelf and be worlds apart in strength. Use a soft, low-grade bolt where a high-tensile one belongs, or skip the washer that spreads the load, and a joint that should last for years can stretch, shear or work loose under vibration.

Nuts, bolts and washers are the fixings you reach for when you need real, adjustable clamping strength through a hole, from a simple gate hinge to a machine base or a structural bracket. This guide explains the main types of nuts and bolts, the washers that make them work, and the two things people most often get wrong: grade and thread. Get those right and you build joints you can trust.

It is part of our wider fasteners and fixings guide. Here we go deep on nuts, bolts and washers.

How a bolted joint works

A bolted joint is a clamp. The bolt passes through a hole, the nut runs onto the other end, and as you tighten it the two parts are squeezed together. Washers sit under the bolt head or nut to spread that clamping force and, in some cases, to stop the joint loosening. Unlike a screw, which cuts its own grip into the material, a bolt relies on the nut, so both ends of the joint carry the load.

Because the joint depends on that clamping force staying tight, three things matter: the strength (grade) of the bolt, the matching thread on the nut, and the washers that protect and lock the joint. We will take each in turn.

Types of bolts and where each fits

KTC stocks a broad spread of bolts for everything from light fittings to structural and machine work. The main types you will meet:

  • Hex bolts: the everyday general-purpose bolt, with a six-sided head driven by a spanner or socket. Used across structures, fittings, machinery and site work.
  • Allen (socket-cap) bolts: driven by an Allen key, with a compact cylindrical head that suits tight spaces and gives a clean, engineered finish. KTC stocks the Unbrako range of high-tensile socket-cap and countersunk Allen bolts, a name trusted for precision engineering work.
  • Carriage bolts: a domed head with a square neck that locks into timber, so the bolt does not spin as you tighten the nut. Common in woodwork and timber-to-metal joints.
  • Eye bolts: a looped head for hanging, lifting or attaching a rope, cable or chain.
  • U-bolts: a U shape with threads at both ends, for clamping pipes, rods and tubes to a surface.
  • Foundation and anchor bolts: for setting into concrete bases to hold down columns, frames and machinery.

Types of nuts and what they do

The nut is half the joint, and different nuts solve different problems:

  • Hex nuts: the standard six-sided nut for general use, matched to the bolt grade.
  • High-tensile nuts: stronger nuts for joints carrying serious load, paired with high-grade bolts so the nut is not the weak link. KTC stocks Unbrako high-tensile hex nuts in common sizes.
  • Nylock (nyloc) nuts: a nylon insert grips the bolt thread and resists loosening under vibration, ideal on machines, pumps and anything that moves or shakes.
  • Wing nuts: shaped for quick hand-tightening without a spanner, useful where you adjust or remove the fixing often, and shuttering wing nuts for formwork on site.
  • Cap (dome) nuts: a closed, rounded top that covers the bolt end for a neat, safe finish and protects the thread.
  • Long (coupling) nuts: extended nuts that join two threaded rods or extend a thread.

Washers: the part people skip and regret

Washers are cheap and easy to leave out, which is exactly why so many joints fail. They do two jobs:

  • Plain (flat) washers spread the clamping force over a wider area. This protects softer materials from being crushed or dented and stops the nut or bolt head pulling through an oversized or slotted hole.
  • Spring washers (grover washers) are split and slightly coiled so they press back against the nut, helping the joint resist loosening under vibration. KTC keeps grover washers in the common sizes alongside plain washers.

As a habit, use a washer under any nut or bolt head bearing on sheet, timber or a soft surface, and add a spring washer or a nylock nut wherever there is vibration.

Grade: the number that decides strength

This is the detail most buyers ignore and most joints depend on. A bolt’s grade tells you how much load it can take before it stretches or shears. Two bolts of the same size can have very different strength.

Steel bolt grades

Metric steel bolts carry a property class, usually stamped on the head, such as 4.6, 8.8, 10.9 or 12.9. A higher number means a stronger, harder bolt. General light work is fine with lower grades, while structural steel, machine mounts and safety-critical joints call for high-tensile grades like 8.8 and above. High-tensile fasteners, such as the Unbrako range KTC stocks, are made for exactly this. The important rule is to pair a high-grade bolt with a matching high-grade nut, so the nut is not the weak point.

Stainless steel grades

Stainless bolts are usually described as A2 or A4. A2 suits general indoor and mildly damp use, while A4 has extra corrosion resistance for wet, coastal or chemically exposed settings. Stainless is about corrosion resistance rather than raw strength, so choose it where rust would be a problem.

When you are buying, tell us the load and the setting and we will point you to the right grade rather than a bolt that only looks the part.

Thread: why the nut must match the bolt

A nut only fits a bolt if the thread matches in both diameter and pitch (how close together the threads sit). Mixing threads is a common cause of a nut that binds halfway or strips.

  • Coarse thread: the common choice for general work. It is more tolerant of dust, minor damage and site conditions, and goes on quickly.
  • Fine thread: more threads per length, giving a slightly stronger grip and finer adjustment, used in precision and machine work.

You will also come across different thread systems, such as metric, and older inch-based systems like BSW and UNC still seen on some fittings and legacy equipment. The safest approach is to match the nut and bolt from the same standard and size. If you are unsure, bring the old bolt or nut to the counter and we will match it exactly.

Material: matching the fastener to the setting

  • Mild steel, zinc plated: the economical everyday choice for dry, general and indoor work. KTC stocks zinc bolts, nuts and washers across common sizes and in mixed-size packs.
  • Stainless steel: for bathrooms, kitchens, exteriors and anything exposed to our Tricity monsoon, where plated steel would rust and streak.
  • Brass: corrosion resistant with a finished look, common in fittings, decorative work and electricals. KTC carries brass hex bolts, nuts and washers.
  • High-tensile alloy steel: for the strongest joints, as in the Unbrako high-tensile range.

A quick note on mixing metals: pairing a plated steel bolt with a stainless nut in a wet setting can cause corrosion over time, so it is best to keep a joint in one material family where you can.

How to read a bolt size

A metric bolt is written as something like M10 x 50. The M10 is the thread diameter, 10 mm, and the 50 is the length in millimetres. A fuller spec may add the thread pitch and the grade. When you buy, the four things worth stating are diameter, length, grade and material, plus the matching nut and the washers you want. Give us those and you will not leave with a mismatched set.

If your bolt runs into a threaded fitting rather than a nut, you may actually want a machine screw, covered in our types of screws guide. And if you are anchoring a bolt into concrete, see wall plugs and anchors.

Quick reference: which fastener for which job

  • General fitting or bracket: zinc hex bolt, hex nut, plain washer under each end.
  • Machinery or anything that vibrates: high-tensile bolt with a nylock nut or a spring washer.
  • Timber-to-metal: carriage bolt, which locks into the wood as you tighten.
  • Hanging or lifting: eye bolt of the correct rated size.
  • Clamping a pipe or rod: U-bolt with nuts and washers.
  • Holding down a column or machine on concrete: foundation or anchor bolt.
  • Bathroom, kitchen or outdoors: stainless steel throughout.
  • Tight space or a clean look: Allen socket-cap bolt.

Frequently asked questions

What is the difference between a bolt and a screw?

A bolt passes through a hole and is tightened with a nut, so both ends clamp the joint. A screw cuts its own grip into the material and usually needs no nut. A machine screw is the in-between case, running into a tapped hole or a nut.

What do the numbers on a bolt head mean?

On steel metric bolts they show the property class, or grade, such as 8.8 or 10.9. A higher number means a stronger bolt. Always pair a high-grade bolt with a matching high-grade nut.

Which nut stops a joint from vibrating loose?

A nylock (nyloc) nut, with its nylon insert, resists loosening under vibration, and a spring (grover) washer helps too. Both are worth using on machinery and moving assemblies.

When should I use stainless steel nuts and bolts?

Wherever there is moisture or exposure, bathrooms, kitchens, exteriors and anything facing the monsoon. Stainless resists rust and staining, while plated steel can corrode in those settings.

Do I really need washers?

Usually yes. A plain washer spreads the load and protects the surface, and a spring washer helps lock the joint. Skipping them is a common reason joints crush the material or work loose.

How do I match a nut to an old bolt?

Bring the old bolt in. Thread diameter and pitch both have to match, and matching by eye is unreliable, so it is quickest to test it against our stock at the counter.

The right grade, thread and finish, matched at the counter

From a single stainless bolt to bulk high-tensile fasteners and grover washers for a workshop, KTC Tools in Panchkula stocks nuts, bolts and washers in mild steel, stainless and brass, including the Unbrako high-tensile range, loose or by weight. Bring your old fastener or tell us the load and setting, and we will match the grade, thread and finish exactly. We serve the whole Tricity, Panchkula, Chandigarh and Mohali, and trade customers beyond it.

Visit: Shop No. 4, Street No. 2, Maheshpur, Sector 21, Budanpur, Panchkula, Haryana 134117
Call: 94175 65977 | WhatsApp: message us here
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