The clamp length is the distance between the bolt head and the nut holding all the components together. It includes steelwork, any shims, plates and washers used. The grip length is the thickness of the steelwork (that includes plates, shims etc.) that can be gripped together by the bolt and nut assembly. It strictly depends on the specific application (how many washers are used in the assembly). Example For EN 14399-3 hexagon bolt assembly type HR , diameter M30 and 100mm in length, the reference clamp length will be between 48mm up to 69mm, whereas the grip length with one washer will be 44-63mm and two washers 40-57mm.
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Apart from dimensional differences ( bigger heads of bolts and bigger nuts on preloaded assemblies), the main difference is in the way how these goods are installed. Non-preloaded bolting assemblies are generally tightened to at least snug-tight. The connected components are drawn together to achieve firm contact without any specific preload. The “snug-tight” is generally referenced as tightening the assembly by one man using a normal-sized spanner without an extension arm until the wrench starts hammering.
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When ordering Preloaded Assemblies (EN 14399-1) to be installed with Direct Tension Indicator Washers (DTIs) , there are 4 different methods of how they can be installed. Depending on the access or preference, you may choose one method, over another. At the purchase stage, we may not know how you will be installing your assemblies. Please read below, as you may require an additional washer(s) to be purchased. Figure 1 Figure 2 Figure 3 Figure 4 Installation methods: Installing DTI under the bolt head when the nut is rotated (Figure 1)
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A single lap joint is a joint with two plates are connected with a single row of bolts. In the case of clause 3.6.1(10) which concerns a single lap joint with a single row of bolts, the bolts require two washers because as the plates are pulled apart the connection bends and the head/nut tries to pull through the plate.
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