Or you can just read the bottle/tube, it tells you the application purposes. I read the tubes and selected locktite blue. The locktite actually serves two purposes, the first being to make the bolt a little less likely to work out on it's own, and the second it helps prevent corrosion on the threads themselves. Anyone who has tried to get old rusty bolts out of anything swears by the stuff (things like trailer lug nuts, U bolts on axles, leaf spring cross bolts, etc). In our case with boats we are typically joining dissimilar metals (aluminum/stainless, stainless/brass, cadmium plated steel (V-frame for mast bracing). All prime candidates for galvanic corrosion.
As far as torque recommendations on screws and bolts, thats all just common sense, if you tighten a bolt and it snaps in half, the next time you know better. Same with locktite, if you assemble something, and three weeks later it works loose, you know to add a little locktite and tighten it a little tighter, you also need to look at the joint, the bolt itself should never be what holds anything together, it's the contact area around the bolt that takes all the force ( bolts are not designed to withstand side force or flexing forces at all). This applies to all bolts, on all applications on everything in use today, not just boats.
The easiest way to get a feel for how tight to tighten things is to take a scrap piece of metal and thread in a bunch of different threads, then take your cordless drill put allen wrenches into the chuck, now drive a screw into the hole, if the screw snaps off, you know it's too much. All the drills have a torque dial, turn the torque dial down and try it again. When you get down to a torque that doesnt snap the bolt, take a sharpie and mark on the drill "6/32", then on the next size screw the screw in until it breaks, then keep turning the torque down until it no longer snaps the bolt, mark on the drill that setting "8-32". Keep going thru all the sizes and mark on the drill housing with your sharpie. When done take your phone and take a pic of the drill, if the drill ever breaks, you can copy the numbers over to the new drill, for example if your "6/32" mark is close to the 8 on the dial, you can safely mark the new drill on the same number (it's all standard torque stuff on most drills).
Now you have the torque specs you requested, these specs apply to everything on the planet (boats, cars, bikes, tv's, toys. swing sets, etc) as long as you follow the correct diameter to length ratio for threads for that particular material. For example steel might be 1.5 to 1, aluminum might be 2.5 to 1, plastic might be 4 to 1. With the first number being the length of thread and the second number being the diameter of the bolt. Every bolt made and every material out there has a different ratio, it's easiest to just memorize them all rather than having to look it up in the machine shop guide (which is a 3 1/2 inch thick book, that you should memorize also), if you don't memorize it, you will wear the book out every 6 months leafing thru the pages. You can forego all the testing if you just refer to the book it has all torque specs for all bolts and fasteners , all materials, all thread types all on nice little charts, the same exact charts are used on cars, boats, wind mills, space shuttles, airplanes, toys, electronics, etc, basically everything on and off the planet. The easiest way is to just memorize it all.
Or you can just ask an Engineer (torque specs are universal and apply to everything in all industries, all products in use today), most can calculate in their head the torque requirements of any material and application based on the tensile strength of the selected material and the desired FOS), if they can't, and they design bridges and sky scrapers, I would find out what bridges they designed and avoid those bridges (just sayin). Look at things like the Brooklyn bridge, which was built in 1870, it's still standing and doing fine, all those calculations were made with slide rules and logarithmic math (before calculators, and computers) so they must know what they are doing.
Hope this helps
Last edited by fusioneng on Wed Sep 30, 2015 6:58 am, edited 1 time in total.