3.1. The minimum material specification for all tubing will be nominal 38mm / 1½" bore steel "blue band" tubing to BS 1387. (This will actually be nearer 42mm / 15/8") This has a minimum wall thickness of 3.2mm / 1/8" and a minimum outside diameter of 48.3mm / 17/8".  See table below for practical imperial and metric stock sizes. Tensile strength will be between 320 - 416 N/mm2.  Yield strength will be at least 195N/mm2. Tubing which exceeds this specification is recommended where the outside diameter at least matches the above type and a minimum nominal wall thickness of 2.5mm where the quality and origin can be traced.”

3.2. All hoops (main and front) and the diagonal shall each be made of one continuous piece of tube. Bracing bars, both rear and diagonal, may be made detachable or jointed as specified later.

3.3. Materials pitted with rust are not permitted.

3.4. Hoop corners must not be separate sections and clamps or angled corners are prohibited. Corners where the tube has flattened or is showing signs of 'crimping' are not allowed, neither are tube ends flattened or crimped for ease of welding. The ratio of minimum diameter to major diameter is 0.9 or greater. Tube ends should be correctly shaped to fit the bar they are joined to. Bend radius must be at least three times the tube diameter.

3.5. Any plugs inserted into the tubing for the purposes of preventing crushing or in the making of joints (see later) will be made from EN8 or equivalent (or better) material.

Below is the table showing the dimensions of permitted materials:-

3.6. (TABLE)

*1387 tube is sold by it's nominal bore, which is known as 40mm / 1½".  (Amended December 4th 2004)

3.7. All of the above are minimum sizes and may be exceeded.

3.8. Welding

3.8.1. Welding should be carried out to the highest standards.

3.8.2. Welds should be cleaned, but not ground or filed after completion.

3.9. Inspection Holes

3.9.1. An inspection hole 3/16" / 5mm diameter must be drilled through every section of tube used.  It should be drilled in a straight length at least 100mm / 4" from a bend and in a position so as to minimise water entry and where it can be seen easily.

3.10. Nuts and Bolts

3.10.1. All nuts and bolts used in securing a roll-cage should be made from high tensile steel.

3.10.2. Plated or corrosion protected / treated nuts and bolts are recommended. Where possible use plated nuts and bolts, the best quality high tensile steel bolt will still rust unless treated.  There is no substitute for getting them with a finish that will not rust; self coloured or black ones come with only a covering of light oil that will soon go and the corrosion problems begin.

3.10.3. All high tensile bolts must have appropriate markings on the head; if it has only manufacturer’s markings or it has a plain head do not use it.  The markings can consist of either letters (UNC, UNF and Whit. threaded bolts) or numbers (Metric or ISO Metric).  The letter to look for is 'S' or a higher letter or the number 8.8 or higher. (For the technically minded, the 8.8 designation is two separate numbers. The first '8' is the tensile strength, i.e. the load at which the material begins to fail, given in units of 100MPa or MN/mm2, giving 800 MN/mm2 or 800,000,000N/m2. Convert this to kg by dividing by gravity (9.81m/s2) say 10, to give 80,000,000kg/m2, and then divide by 104 to convert to cm2 which gives 8000kg/cm2 or 8 tonnes/cm2.  The second part of the designation ‘.8’ is then used to generate a decimal fraction of the first part, i.e. 8 x 0.8 = 6.4 or 640Mpa, 6.4 tonnes/cm2. This is the yield strength, i.e. the load at which plastic deformation of the material occurs.)  Stainless Steel bolts usually have a tensile strength of 5 Tonnes/cm2,  33 tons/in2 (marked A2 for Stainless Steel and 'M' for the strength) so be warned!  Some bolts may be marked in Newtons per square centimetre, in which case high-tensile means over 80N/cm2. Do not get confused with the manufacturer's name code, e.g. GKN, SN, BP, etc. High tensile bolts must always be fitted with high tensile nuts, and these will also have appropriate markings. Usually, there will be a marking on the face (not the flat) of the nut and this may be out of sight when fitted depending which way up you screw it on. Nyloc nuts are often plated but should still show this mark;  you don’t have the option which way up this type of nut goes and this mark will not be visible on assembly.  A figure 8 will equate to a grade 8 specification and must be used with a grade 8 bolt. Nuts may also have a “clock code”. There may be a dot and a stroke. With the dot at the top (12 o’clock position) look to see where the stroke is. A stroke at the 8 o’clock position indicates a grade 8 nut. You must be able to prove to a scrutineer that the nuts and bolts used meet these specifications. If in doubt, ask the supplier for a chart that shows the meaning of the markings.

3.10.4. Plain nuts must always have lock nuts or they must be self locking types.  There are several of these ranging from 'Nyloc' to 'split ring' types.  Alternatively, use castellated nuts and split pins or tab washers.  You must always use a washers under the nuts and these should be suitable for the type of nut.

3.10.5. Also remember, a set screw with the thread running from tip to the head is not a bolt (which has the thread running from the tip to the shank - approx. 2/3 the length of the bolt) and is not designed to bear a shear load.  The plain shank is designed to do that, a thread is designed to use the nut on.  Drill the holes to fit your bolts (or buy your bolts to fit the holes!) and do not have any gaps round them.

3.10.6. Bolt (and other material) sizes shown in this book are given in Imperial and Metric sizes.  For nuts and bolts, you may not be able to get 9.6mm, (3/8"), for example - always get the next largest 'whole' number size, e.g. 9.6mm = 10mm.

3.10.7. The following table may be helpful.

Imperial (inch)	Metric (mm)	ITEM
1/8	3	Tube wall thickness
3/16	5	Bolts
1/4	6	Bolts & Plates
5/16	8	"
3/8	10	"
1/2	13	"
9/16	15	"
17/8	48	Roll-cage tube
2	50	"
12	305	1 foot
36	915	3 feet / 1 yard.

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Last Updated:
18/02/2007