Look closely at your barbell the next time you’re in a gym. Much of the surface is roughed up with a diamond pattern. This is called the knurling, and it helps your grip. But near the ends of the handle, you’ll see a ring or line of smooth metal on each side. Maybe two on each side, actually. These aren’t just for…
Source: LifeHacker – You Should Be Paying Attention to Those Smooth Rings on the Barbell