Similarly a grade 8.8 bolt will not snap until it is carrying a load of 80kg per square millimetre. In round terms it is in 10’s of kg per square millimeter of the bolt cross second.įor example, a grade 12.9 bolt will not snap until every square millimetre of the bolt cross section is carrying a load of at least 120 kg. The first number gives the breaking strength of the steel in the bolt. Usually the markings are on the top of the bolt head but sometimes they are on the side.
Model t sparkbox nuts size code#
The bolt head should also have a code – normally two or three letters – indicating the manufacturer.
Model t sparkbox nuts size full#
On the head of each bolt are two numbers separated by a decimal point, the full list includes ten grades from 3.6 to 14.9 but in plant and machinery only grades 8.8, 9.8, 10.9 and 12.9 are normally found.
This short guide is intended to give you the information you need to be able to correctly identify and use the metric nuts and bolts most commonly found in plant and machinery.Įxcept for the very lowest grades, metric nuts and bolts all carry identification markings which indicate their strength. If you are responsible for repairing and maintaining machinery, particularly if that machinery is involved in lifting operation or other safety critical applications then you will be aware of the importance of fitting the right parts in the right way. The difference in strength between different grades is quite dramatic: the highest standard grade being capable of carrying more than three times as much load as the lowest grade. The situation on is almost as complex with metric nuts which come in a wide variety of types (full, thin, nyloc, castellated….) and 5 strength grades as well as the same range of sizes. There are nineteen standard sizes – known as the ‘preferred ‘ sizes and ten less commonly used (the so-called ‘non-preferred’) sizes. There are no fewer than 5 different threads for different applications and 10 different standard strength grades defined for each size of bolt. In fact, of course, nothing could be further from the truth. It is intended for those working in plant and machinery maintenance to give enough information on to ensure that correct replacement parts are identified and used.įew parts are as critical in the assembly of modern machinery as the nuts and bolts which hold it all together and, at first sight, it seems that all metric bolts are basically the same. This short guide is intended to give a very basic introduction to ISO metric nuts and bolts.
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