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Socket head fasteners with flank drive tightening features

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There is a fondness for using socket-head screws in race engines. They are neat, and one can use a number of them close together, allowing the use of high clamping forces. Taking the example of adjacent 6 mm metric screws, two socket-head types can comfortably be placed 10.5 mm apart, whereas two hexagon-head versions need 11.54 mm, plus tool clearance to allow for a socket or a wrench, between screw centres. In many circumstances, socket-head screws also have advantages in terms of tool...

Nut design for increased fatigue resistance - 2

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In the previous article, the subject matter was the work done in the former USSR on fastener fatigue and particularly the positive effect that nut design and material selection can have on the fatigue life of studs and other male fasteners. In this article we will look at attempts by fastener manufacturing companies to achieve the same effects using relatively subtle changes in the fastener geometry. There have been several attempts to manufacture nuts with a thread form that distributes...

Nuts: design for increased fatigue resistance

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Nuts are often given little consideration in design, especially compared to the stud onto which they engage. The reason is quite simple: nuts rarely fail unless they are completely unsuitable for the job. What is less commonly understood though is the fact that the nut design can have a critical effect on the fatigue resistance of the stud onto which it fits and the pre-load in which it is responsible for, in cases where stud failure coincides with the first loaded threads in the nut....

Anti-rotation washers

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There have been a number of articles about fasteners that have mentioned friction, and as we have discussed, this has an important effect on the relationship between tightening torque and tension. Although torque-based tensioning of fasteners is not ideal, having a large number of unpredictable variables, we often don't have much choice other than to use this method. The torque-tension relationship relies on a number of geometric parameters that are often under our control, or are...


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When we talk about friction in regard to race engines, we are normally referring to the power or energy lost due to it, but the phenomenon of friction plays an important role in the function of many components in a race engine. Fasteners are a particular example. For critical applications, we would ideally like to measure the tension in a fastener directly, but this is rarely possible. Our next best method of gauging the tension in a fastener immediately after tightening is to measure its...