A thread pitch gauge can be a handy tool, but not in this case. A threaded bottom bracket on a Bianchi is going to have either English or Italian threading, and both standards use 24 tpi threads.

There are a few ways to tell English and Italian bottom brackets apart, though:

• English bottom bracket shells are 68 mm across. Italian bottom bracket shells are 70 mm across.
• The drive-side cup on an Italian bottom bracket is right-hand threaded, meaning you'd turn it clockwise to tighten. The drive-side cup on an English bottom bracket is left-hand threaded.
• The diameter of an Italian bottom bracket is slightly larger than an English bottom bracket. English bottom brackets are 1.37 inches across (about 34.8 mm) while Italian bottom brackets are 36 mm.

Anyway, as mentioned above, if the bike already has a bottom bracket installed, it probably has markings that can be used to identify it -- either by model or by size/threading. Or, if the frame has some identifiers like a model name or tubing type, that might be enough to identify what bottom bracket it'll use. (If the tubing was made by a Japanese company like Tange or Ishiwata, the bottom bracket will almost certainly be English threaded.)