When through bolting hardware, you might not pay much attention to which direction the bolt is facing. This may seem like a very mundane point to ponder, but this small detail can have a significant effect on the outcome of your project.
You may feel inclined to simply insert the bolt from which ever side you are standing on, but the truth is there is a right and wrong way to position a bolt.
To begin, lets look at a standard bolt. You have the head, smooth shank, and threaded portion. The head allows you to grasp the bolt with tools such as wrenches and sockets. The smooth shank is often overlooked, as it merely connects the head to the threads. The threaded portion is where the opposing nut attaches to give a bolt its fastening abilities.
The truth is, the smooth shank that is often ignored is actually the designed load bearing area of the bolt. This region of the bolt bears the most bulk and thus strength of the bolt. The threaded portion is actually significantly thinner as the threads are cut in, making the thickness of material reduced by the depth of the threads.
If you through bolt a high sheer stress object with the nut facing the most load, you risk sheering off the nut and causing a catastrophic failure to whatever you were trying to retain. The head should face the high strain working areas, as the head is right next to the smooth shank and thus is the strongest side of the bolt.
In the example below, a bracket was through bolted to the mast that will act as the attachment for all the turning blocks. Under full load, this bracket will be subjected to the full fury of the reef lines and main halyard. Since the halyard is located on one side of the bracket, that side will also be bequeathed with the heads of the bolts. The other side which will be under slightly less load will contain all of the acorn nuts used to hold the bolts in place.
Next time you go to through bolt a piece of equipment, be mindful of which end will be subjected to the most strain and place the heads of the bolts accordingly.
