Which bottom bracket do I need to replace crank on a Trek FX 7.1? I have a Trek FX 7.1 that I've rode for several years now and replaced parts as they've worn out.

Now I'd like to upgrade the whole drive train with Tiagra 2x10 flat bar shifters, derailleurs, crank, cassette, wheels, etc.

So, my question is, which bottom bracket do I need to replace the old one? There are choices of english thread or italian thread and 68mm or 70mm. Additionally, if there is a higher quality one someone would recommend over the taigra one, that would be appreciated. Please specify size and thread needed.
Assuming that you own the 2012 model, your bottom bracket should be a Shimano M171, according to the Trek Archives.

Found a Shimano Technical document that says you should have a 68mm thread width.