Some people are into using Acupuncture Needles as a stimulus for sex. These are dangerous if you don't know what you are doing.
BDSM users will often put these in a woman's breasts. It believed they can be used by knowledgeable practitioners placed properly to bring pleasure.
Sold over the Internet ranging in size from 30 to 40 gauge (0.30mm to 0.16mm).
Approximate cost: $24.00 per box of 500 needles.