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Front caliper star head bolts

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Cheers guys, never heard of a "bi hex" before, any particular reason why they are used?

There are more drive points, or contact points, between a 12 point socket and a 12 point bolt head, thus the load while tightening is spread over a larger area. Look at the tightening torque, you will find it's quite high for a bolt-head of that size. In some instances you will find that, for reasons of access, the head is a smaller size than that normally associated with a bolt of the same diameter. You have to put a higher than normal torque through the head, but in this case it's because the head has been reduced in size, rather than the torque setting being high in relation to the bolt diameter.

There is nothing 'special' about the sockets at all, bi-hex (12 point) sockets have been in standard use in the UK for decades. This was purely because when you present the socket to the bolt the socket has to turn a maximum of half the distance before engaging with the bolt head or nut, compared to using a 6 point socket. This sounds a very minor point, but look at your standard sockets, whichever style you have at the moment you will notice a difference if you change to the other. This change is more noticeable changing from 12 to 6 point.

The possibility here is that the introduction of 12 point sockets date from when most mechanics used a preponderance of hand tools. Now there are so many powered tools around (air and electric) it's possible this has made the stronger 6 point socket the preferred design.

In North America they seem to have stayed with 6 point sockets, receiving the shock you have found when they first hit Land Rover engineering practice.

As an aside, you may notice that Land Rover frequently use higher torque settings than other manufacturers in similar instances. Top bolts for front shock absorbers on the 38A is a case in point. This is not just a case of 'making the bolt harder to undo'; the loading imposed on the on the complete assembly by the high torque setting makes it more rigid and thus less likely to distort under load. There are several instances in the Technical Bulletins when the answer to a problem is to revise upwards the tightening torque, sometimes upgrading the bolt to achieve this.


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