Square tapper bottom bracket spindles are either JIS or ISO but there are many different threading of bottom brackets, ISO, French, Italian etc etc.

It is advised that you use the bottom bracket that the company of the crankset suggest; both interface type(JIS/SO) and spindle length. You need the correct spindle length to have your chainline as straight as possible.

Width is determined by the frame, measure your frame's bottom bracket shell. You'd need a bottom bracket that is the same width as the shell. In your case, a Gazzetta, which use an ISO/English threaded bottom bracket, you'll need a 68x1XXmm bottom bracket. The latter number represents the length of the crankset, which again, determined by the crankset.

Reading Sheldon's article on bottom bracket might help a bit.