Bolts and Screws

Bolts are externally parallel threaded, headed mechanical fasteners designed to be used with either a nut or into a threaded hole to generate a clamp load. The prime function of a bolt is for the assembly of two unthreaded components, with the aid of a nut. Bolts have a plain unthreaded portion of the body acting as a dowel, pinning the joint against sideways shear forces.

Using bolts in taped holes is unusual and in customarily reserved for hexagon screws that are threaded all the way to its head and have a component that contains its own thread; a screw must always be turned to assemble the joint.

Bolts and screws use a wide variety of head designs the most popular being hexagon and square; they are designed to engage with the tools used to tighten them. There are some instances where the head is designed to lock the bolt in place, stopping rotation; a spanner or a turning device is only needed to rotate the nut end of the assembly, a typical example is a carriage bolt.



Hexagon Bolt and Screw        Square Bolt    Hexagon Flange Bolt     Serrated Hexagon Flange Bolt  

Carriage Bolt       HSFG Bolt        XOX      Square-Square Bolt       Plough Bolt   

Bolt family








Hexagon Head Bolt and Hexagon Screw

Hexagon head screws and hexagon head bolts are the most popular fastener product and are obtainable in Metric, British inch and American Inch threads. Bolts and screws are available in a range of strength classes or grades and materials.  The manufacturer's identification letters or symbol is mandatory if the strength grade is marked on the head.

In the USA hexagon bolts are called hexagon cap screws, and full thread hexagon set screws are called hexagon tap bolts.

HEXAGON BOLT                HEXAGON SET SCREW                                             

Hexagon bolt   (Europe)                                            Hexagon set screw (Europe)

Hexagon cap    (USA)                                                Hexagon tap bolt     (USA)





High Strength Friction Grip EN14399

Non-preload hexagon bolting assemblies have to be supplied in accordance with BS EN 15048

Preloaded Hexagon bolting assemblies in accordance with BS EN 14399

To adhere to the CE marking requirements. Assemblies need to be labelled in accordance with the standard and regulatory requirements and supplied with the required documentation. 





Flange Head Hexagon Bolt and Screw    


Flange head hexagon bolts have a forged flange under the hexagon head spreads the bearing face load and eliminating the need for a washer. As with hexagon bolts, the manufacturer’s ID and strength grade should be shown on the head, if there is none it is a very low-grade product similar to a machine screw. Non-standard flange head bolts are common with large and thicker flanges or non-standard drives.






Serrated Hexagon Flange Bolt



Flange head hexagon bolts can also have a formed flange with serrations. The flange spreads the load, and the serrations act like a serrated locking washer, locking the bolt in place.




Square Head Bolt


The first hot forged bolts had square heads, today they are both formed and forged. Square bolts are still readily available, though less common than the hexagon bolt. These are held and turned by a spanner or wrench, of which there are many forms. Most are held from the side, some from in-line with the bolt. The construction market is the biggest consumer.





Carriage Bolt, Cup-Square Bolt


The carriage bolt is a popular name given to the mushroom head, square neck bolt, also known as cup square or coach bolts not to be confused with coach screws.

There is no drive on the head, and they are usually supplied with a hexagon nut, both assembled and unassembled. The square profile under the head is designed to locate with a mating square hole in the construction material, resisting rotation when the assembly is tightened using the nut and allowing tightening from one side.

They are usually made from mild steel in strength grades 4.6, 4.8, 6.8, and 8.8 also are available in stainless steel. Carriage bolts should be marked with the manufacturer's I.D. and the strength grade on the head.

Some carriage bolts used in the construction industry are required to conform to the Construction Products Regulation  they are expected to be CE Marked, supported by a manufacturer’s Declaration of Performance 





Mild Steel XOX & Low Strength Structural Bolt


Traditional mild steel hexagon head bolts and are manufactured in ISO strength class  4.6, 4.8 and 6.8.  XOX is the abbreviation for a heXagon bolt with rOund neck and heXagon nut.

Some Black bolts used in the construction industry are required to conform to the Construction Products Regulation they are required to be CE Marked, supported by a manufacturer’s Declaration of Performance.

Structural bolts are designed for use in structural steel applications and have a special short thread length of 1½ times the nominal diameter of the bolt. Black bolts are becoming difficult to find and are being replaced by cheaper and more readily available standard 8.8 high tensile bolts and screws.




Square-Square Holding Down Bolt


Square-Square Holding Down Bolts are a UK specification product, manufactured to British Standard BS 7419 in strength grades 4.8 and 8.8. They are typically supplied with Mild Steel Plate Washers, usually square in shape although other dimensions are available, and with Waxed Cardboard cone Boxes.

They are used to locate structural steel columns into a concrete foundation. The bolt is set loose in concrete, the bolt cone boxes allowing adjustment, so the bolt fits the holes in the baseplate of the column.





Plough Bolt Plow Bolt


Plough bolts and screws are the UK names given to flat or slightly round countersunk head square neck bolt and screws. Their design is to meet applications requiring a smooth final surface from which the bolt head may not protrude as it will damage surfaces and wear rapidly.

They are used to connect snowplough blades and blades or buckets on a wide range of heavy construction equipment including bulldozers and excavators.

There is no drive form on the face of the head, and the square neck prevents rotation during tightening of a nut.





Bolt family

This is a linked list of the family of bolts each link will take you to an image and further information; if the product is not high lighted you can search for it on site.


12 Point Bolt    Banjo Bolt  Blade Bolt    Blind Bolt   Cam Bolt    Cap Bolt  Countersunk Bolt 

Countersunk nib Bolt  Cup Head Bolt    Elevator Bolt   Eye Bolt   Fit Bolt   Foundation Bolt 

Hanger Bolt   Hook Bolt   J Bolt   Jack Bolt    Oval liner Bolt   Oval mine Bolt   Place Bolt   

Roofing Bolt   Saddle Bolt   Security Bolt   Shear Bolt   Shoulder Bolt   Silo Bolt   

Spade Bolt   Step Bolt   Structural Bolt    Taper Bolt   Tee bolt   Tension Bolt   

U bolt   U Bolt Saddle   Wheel Bolt