While the stem plays an important role connecting your handlebars to your bike, the stem actually plays a vital role in terms of comfort and handling. The length and angle of rise which the stem provides can make the difference between comfort and discomfort, particularly as you spend more time on your bike. Most stems and bars are 31.8mm diameter fitment, also check the fork to stem fitment diameter, usually an inch and an eighth. A torque wrench is a useful tool for fitting a stem without overtightening and stripping the thread.