When mounting a stem, often it is so snug that it's a hassle to get on and off. Even if you back the clamping bolts out, it can still be so tight you may scrape up your steer tube in the process of mounting it. There's an easy trick to fix this, and all you need is a penny.
The 'Ol Penny Trick
First, take out the clamp bolts. At this point, sticking a screwdriver in the gap and twisting it seems like a good idea. It will probably have the effect of separating the clamp, but will often tear up the soft aluminum. (look at my brake levers for a frustrating example of this...) A safer option for your anodization is to take one of the mounting screws, and thread it into the clamp from the opposite side, and then slide a penny into the clamp gap covering the screw hole. Tighten down the clamp bolt until it makes contact with the penny, and then continue to turn it and it will spread the clamp.
Spread the stem
You can then take the penny out, as after spreading the stem usually fits better. If your stem is carbon, you should use extreme caution with something like this, as you can crack brittle materials by point loading them. Now just put the bolt back in the right way, easily put your steam and put the penny back in your piggy bank.