The amount of bolt or capscrew that can stretch and act as a spring is important for keeping the fastener tight. I think sone engineers at Caterpillar have determinrd that 19 mm is the min. free length ( dist. from conact surface of head to the start of the nut or tapped hole threads )for grade...
The Military has a lot of data from dropping things out of airplanes. There are some mil specs for rigging heavy equipment for air drop and I think most are on line but I do not remember where.