HV bolts nuts and washers

[67bonnie]

Can anyone explain to me what the differences are between standard metric grade 10.9 bolts and bolts marked as "10.9 HV"? I found the EN 14399 standard that seems to suggest that these fasteners are designed for "preloaded joints", but that makes no sense to me because all bolted joints are preloaded to some degree.

 

[CoryPad]

Yes, EN 14399 is the correct set of documents. Those standards identify requirements beyond basic composition and mechanical properties. Here is a good overview document:

http://www.bapp.co.uk/wp/wp-content/uploads/2009/04/bs-en-14399-parts-1-to-8.pdf

The reason that "preloaded joints" is identified is because for large structures (buildings, bridges, etc.), it is common to have joints that are just snug tight (little preload), for example.