How to choose bolts and metric screws: diameter and material

A bolt or metric screw is chosen from five pieces of data: diameter, length, head type, material and strength class. The material decides where you can use it: galvanised steel is fine indoors or in mildly aggressive environments, stainless steel where there is damp or outdoors. In the collection diameters range from 2 to 12 mm and above for wing screws, lengths from 16 to 100 mm for screws and up to 160 mm for TED bolts.

The types

• Hexagon head bolts: the TE and TED bolt series, like the TED 12x100 bolts. They are tightened with a spanner and a nut; the designation 12x100 gives the diameter and length in mm.
• Galvanised and stainless steel metric screws: with different heads and drive types (Phillips, Pozidriv, Torx, hex socket). The stainless ones, such as those in A2, are used where galvanised steel would rust.
• Hammer-head bolts: for channels and profiles, like the Fischer FHS 31 Clix hammer-head bolt.
• Wing screws (thumb screws): tightened by hand without a spanner, useful where parts are opened and closed often.
• Spacers and spacer nuts: they hold two parts at a fixed distance, for example the male-female spacer nut.
• Split pins and spring clips: spring cotter pins with a single or double eye, and assortments, to lock a pin or a bolt.
• Screw caps: they cover the screw head for a neat finish and protection.

How to choose by job

The features to look at

Diameter and thread. The nominal diameter (M6, M8, M10, M12) is the size that must match the threaded hole or the nut. In the collection you will find, for example, M8, M10 and M12.

Length. Measure the length of the part to be passed through and add the thickness of the washer and nut. In the collection lengths range from 16 to 100 mm for screws and up to 160 mm for bolts.

Drive type. This is the type of head recess: PH (Phillips) and PZD (Pozidriv) for cross-head screwdrivers, TX for Torx, EI for hex socket, CH for the spanner size. Use the exact tool, otherwise the head is damaged.

Material. Plain steel, galvanised, white zinc-plated, A2 stainless steel. The more exposed the joint, the more corrosion resistance matters.

Strength class. For steel fasteners you will find classes such as 8.8 or 10.9. If the joint is structural, the class is marked on the head and must be respected.

Standard. In the collection you will find DIN 931 for hexagon head bolts, and DIN 601, DIN 94 and UNI 1336 for the split pins. Check the one stated on the product page.

Pack size. Screws and split pins are sold in packs of 4, 50, 100 or 200 pieces.

Common mistakes

• Mixing galvanised and stainless steel in the same joint outdoors. Contact between different metals, in the presence of moisture, promotes corrosion.
• Choosing a screw that is too long or too short. Too short: not enough thread engaged. Too long: it sticks out and can get in the way.
• Tightening beyond the specified torque. The thread is damaged or the screw breaks.
• Forgetting the washer and lock nut where there is vibration. Without them, the nut works loose.
• Using the wrong tool on the recess. A Pozidriv forced with a Phillips ruins the head.

Frequently asked questions

What does 12x100 mean?

A diameter of 12 mm by a length of 100 mm. For TED bolts, this is the size given in the name.

Galvanised or stainless steel?

Galvanised indoors or in mildly aggressive environments, stainless steel outdoors or where there is damp. Stainless steel costs more but does not rust.

What is the difference between TE and TED?

They are two series of hexagon head bolts in the collection. For the differences, check the product page of the individual item.

What is a split pin for?

It is pushed through the hole in the pin or bolt and opened out, to stop the nut or pin from coming off.

To see the sizes available, open the Bolts and Metric Screws collection and ask for a quote or advice from the AMES technicians.