Screws and Fasteners: Buy Screws Online

Amongst the bewildering array of screw types and sizes available, it can be difficult to pick the right ones for the job. Whether you are looking to buy screws online for a specific job, or you want a handy selection of screws and fasteners for your toolbox, choosing between steel or brass screws; Phillips or slot; or countersunk or flush is complex, before you even think about the right size. In this handy ‘buy screws online guide, ‘you will learn a little about the various categories and subcategories of screw, making your online shopping a little easier.

Screws are available in a range of materials and finishes, and have different heads to suit specific tasks, whether you want a general woodscrew or an ornamental brass screw. Most screws are made from mild steel, but stainless steel and brass are perfect options where corrosion and rusting is a concern, and hardened steel screws are perfect for tough jobs, such as masonry or self-tapping into hardwood.

In many situations, screws are a far better option than nails, providing a stronger join and also allowing a far higher degree of precision, often crucial for fine carpentry or metalwork. Using screws allows you to disassemble joints quickly without damaging any components and, if allied with glue, screws make a strong joint that will last for many years. In areas where potential physical damage is possible, directly or through vibrations, such as windows and French doors, or near ceramics or plaster, screws are the only choice.

Mild Steel Screws

By far the cheapest and most common type of screw is made from mild steel, which is cheap to buy and is adequate for most jobs. Try to avoid the temptation to look for the cheapest option, as very soft screws have a tendency to snap or the slot can become worn, especially if you use an electric screwdriver or portable drill for speed.

Hardened Steel Screws

Hardened steel screws are a little more expensive, but their rugged construction sees them as the perfect choice where extra strength is required, and their load bearing capacity is far superior to their mild steel counterparts. Hardened steel is perfect for use with masonry and concrete and, for many materials, including softer woods; hardened steel screws can be driven directly into the wood without the need for pilot holes.

For hardened steel screws, especially when using power tools, you need to ensure that you have a good quality screwdriver head, to prevent wear and tear. The high-carbon steel used for these screws is particularly prone to corrosion, so many manufacturers offer coatings for extra resistance.

Stainless Steel Screws

Stainless steel screws are perfect in areas where dampness and corrosion are a genuine concern. For external use, where they will be exposed to the elements, such as for fixing guttering or in marine environments, stainless steel screws are rustproof and reasonably strong, with the added bonus that they are recyclable.

Stainless steel is perfect for working with woods, such as redwood and cedar, with a high tannin content, because the tannin can chemically react with standard steel, causing it to become black. Because stainless steel is not as strong as the standard steel, use longer, heavier screws wherever possible.

Stainless steels are graded with a three digit SAE Stainless Steel Grade number beginning with 3 (303, 316), or with a number such as 18/10, 18/0, which refers to the percentages of chromium and nickel in the alloy. In marine environments or for precision engineering, it is often wise to look for higher quality, 316-grade stainless steel rather than 305 or 306.

Brass Screws

Although brass tarnishes, this is much less of a problem than with steel, and brass screws have the advantage that they look nice. For piano hinges or door furniture, they are an excellent choice where appearance is crucial. However, brass is a much softer metal than steel, so they are best avoided for heavy load-bearing tasks.

Galvanized Screws

Galvanized screws are made from mild or hardened steel and are coated with a corrosion proof layer, usually zinc or chromium. The downside is that the coating can chip, exposing the steel to corrosion, but they are stronger and much cheaper than stainless steel, making them perfect for decking or fencing.

Hot-dipped galvanized screws: These are the sturdiest type and can handle rough treatment. The disadvantage is that the coating is rough, making them difficult to drive, and Phillips and square head recesses often become filled with the coating, making them difficult to engage and ensuring that you will have to reject a fairly high percentage of screws. Despite this, these screws are excellent where corrosion resistance is the prime concern, lasting for 15 – 20 years, even in the harshest climates.

Mechanically Coated Screws: These have a thinner coating than the hot-dipped screws and they do not suffer from the same problem with irregularity. However, they are not as robust and are prone to corrosion, especially if the finish chips.

Electroplated Screws: Cheaper than the other types, the coating of these screws is easily damaged, so they are not suitable for heavy work or harsh climates. However, for indoor use, they are a decent choice.

Coated Screws: As a cheap alternative, screws coated with paint, ceramic, polymer, or epoxy resin are a good choice, as they are smooth and easy to use. The tough, durable coating prevents corrosion, and they are a better option than galvanized screws and match stainless steel under most circumstances, although stainless steel is better for marine environments.

Epoxy and ceramic coatings are extremely tough, making these screws perfect for high-stress conditions, but the coating can chip, allowing moisture to attack the bare steel. Paint and epoxy are a little more resistant to chipping but wear more quickly. Ceramic screws, especially japanned screws, are perfect for decorative purposes, such as ceramic address plaques and porcelain door handles.

There are four main types of screw head, and the choice is largely based upon personal preference.

Slot Head Screws

Slot head screws are the familiar old-fashioned type, driven in with a flat screwdriver and common in woodworking and wood exterior doors. The disadvantage is that screwdrivers can slip out of the slot, especially with power tools, and the rough edges are a problem under some circumstances, especially mechanical applications, but slot headed screws can handle a lot of torque without damaging the head of the screw.

Phillips Head Screws

Phillips head screws have the distinctive cross-pattern, and the head of the screwdriver is less likely to jump out of the slot when tightening the screw. However, for high-torque use, the Phillips type head can cause the screwdriver to lift out of the slot, called a cam out.

Posidriv Screws

Like the Phillips head, the Posidriv screw is cruciform, but it has four smaller spokes for added grip. The design of the screw, with straight-sided slots, ensures that the chances of camming out are much less, so these screws are good fro high-torque situations. The Posidriv and the derivative Superdriv are a good choice, but the downside is that they are often mistaken for Phillips screws, and people use the wrong driver heads – this is fine in most situations, but will damage the screw if heavy force is applied.

Square Drive/Hex Head Screws

The original square drive ‘Robertson screw’ simply incorporated a square hole in the head of the screw. These screws have little risk of cam out, and the fact that you can apply a lot of torque makes them popular in many applications where strength is important.

Due to an issue with licensing rights, square drive screws never achieved widespread popularity or geographical spread, so they were largely superseded by the hex head screws and Torx screws, which use an Allen key driver head to give the same advantages. Because there is little chance of cam out, they can be used with an Allen key or wrench, and the design is perfect in areas where space is restricted.

Combination Heads

There are many subvariations, including tamper-resistant screws, but one particularly common type is the combination Phillips/Slot screw, which can be engaged by slot or Phillips drive. This is convenient in many situations, ensuring that you always have the right tool to hand, but the compromise often means that it is difficult to apply a lot of torque, so they are popularly used by electricians, where strength and load bearing are not the major concerns.

As you can imagine, there are many different measurements used around the world for the different types of screw. However, one measurement that is generally the same is the gauge, or the thickness of the screw. This is expressed as a number from 1/20, with 4, 6, 8, and 10 the most common.

The length of the screw is measured from the top of the head in countersunk screws and from just underneath the head in other types, and this is measured in inches or in millimeters.

The other important measurement is the thread count, expressed as threads per inch. A high number indicates that the screw will grip the substrate firmly and provide a great deal of strength, but it will require more effort to engage. By contrast, a low number means that the screw is easy to insert with a minimum of effort, but this is at the sacrifice of load bearing potential.

To summarize, screw sizes will often take the form:

4-15 x 41/2 fh

This is a 4-gauge screw with 15 threads per inch, four and a half inch length, and flat head type.

Screw Types

There are four main types of head for screws, flat, round, oval, and pan head.

Flatheads

As the name suggests, have a perfectly flat head that will fit flush to the surface of the material. However, these screws require a countersink hole to be drilled after the pilot hole, increasing the work required.

Roundheads

These have a semicircular profile, and are useful where the screw is likely to be removed or if the surface of the substrate, such as sheet metal or glass, is too thin for countersinking. Roundhead screws often find use in door hardware, as a decorative addition.

Oval Head

These are a combination head, consisting of a roundhead with a countersink, and they are often used for woodwork or where the screws will be a decorative feature.

Pan Head

These screws, with a large, flat head, are often used where the substrate is thin or delicate, providing maximum grip without causing damage. Roofing and sheet metal screws are often of this type.