This article is from the Piercing FAQ, by Anne Greenblatt with numerous contributions by others.
4 to 6 weeks
The horizontal hood piercing is made through the pronounced vertical
ridge of hood tissue approximately 3/8" to 1/2" above the edge of the
hood. The horizontal piercing does not pass through the hood
itself. Some women do not have enough loose tissue to support this
piercing. The clitoris and hood tend to retract when standing which
may make the horizontal piercing uncomfortable or inappropriate; the
position of the piercing and the ring dimensions should be selected
Placement of the piercing and selection of the ring dimensions should
be made so that the bead rests on the tip of the clitoris. The
horizontal piercing is most stimulating if the clitoris is exposed. If
the clitoris is not exposed the wearer may not feel the ring unless
pressure is applied to the jewelry. Larger beads (7/32" to 1/4") are
more stimulating because of the greater weight and surface area.
The ring, as it passes through the piercing, can stimulate the shaft
of the clitoris when pressure is applied. Larger gauge rings are more
stimulating in this manner.
Initial jewelry: Captive bead rings in 14 to 10 gauge and 3/8" to 1/2"
in diameter; the diameter should be at least 1/8" wider than the width
of the piercing.
A thicker gauge should be considered if the wearer enjoys pressure or
friction during sex. A thicker gauge will be more comfortable and less
likely to pinch or tear.
Women with a narrow pubic area and/or large outer labia or whose
thighs compress the pubic area may find this piercing uncomfortable
because the ring will have a tendency to twist. In this case, a
symmetrical teardrop shaped ring is often more appropriate than a
round ring. The tapered shape of the ring prevents it from getting
caught between the outer labia and painfully twisted and pulled which
can cause the piercing to migrate or tear during healing. Most
frequently used dimensions are 3/8" wide x 1/2" long and 1/2" x
5/8". Wearing a thicker gauge will also reduce the risk of migration
or tearing caused by twisting of the jewelry.