Folding garden chair assembly...putting a stud in the wood
The stud gets screwed into the wood piece by using a tool that grips onto the smooth cylindrical part of the stud. That could be any of the following types of tools:



(Pictures from Irwin Tools web site. Other brands of similar tools available too).

In some cases the stud will be relatively soft steel and the tool could mar the smooth surface of the stud. In this case you can try wrapping a strip of leather around the stud and then use the tool to grip the stud through the leather. A strip of rubber can also be used but I have found the strip of leather to work better for this. The right most type of tool shown above can be adjusted so that it can firmly clamp onto the stud and then be used to turn the stud into the wood piece. The other two will gain grip while you hold the handles together.