"A PA is probably the most common male genital piercing -- it heals quickly and is relatively trouble free. It enters the urethra and exits immediately behind the glans.
The piercing is usually done in 10ga or larger, and stretches very quickly. Most men (and women) find that 6ga or 4ga is an ideal size. For some people, the piercing is purely aesthetic, but for others, it is highly sensual. I should add that some women find the piercing uncomfortable.
Finally, be warned that wearing a ring in your urethra will often affect the urine stream -- you may need to sit down to pee."