This article is from the Piercing FAQ, by Anne Greenblatt with numerous contributions by others.
Because most men have very small or flat nipples, the piercing is
usually made behind the actual nipple and through the areola. Most
piercings are between 3/8" and 7/16" wide. Nipples which are
pronounced and wider than 1/4" can be safely pierced through the base
of the nipple.
If the nipple is completely flat and cannot be easily pinched, the
tension of the skin creates pressure on the jewelry which may cause
the piercing to migrate or even reject completely. Often, the nipple
is more easily pinched vertically, in which case a vertical piercing
is more likely to be successful. In some cases, the nipple is more
easily pinched at a diagonal, or perpendicular to the long axis of the
nipple. In some cases the piercing will shift or migrate slightly
while healing but will eventually settle. The piercing should not be
made excessively deep on the assumption that it will migrate into
Initial jewelry: Captive bead rings in 14 to 10 gauge and 1/2" to 3/4"
in diameter; the diameter of the ring should be at least 1/4" wider
than the width of the piercing.