Adapted from Wikipedia
Penis banding is the act of placing a constrictive material around the penis. The general goal is to decrease functionality of the penis by damaging nerves and other tissues in the penis.
This is accomplished in two ways: by reducing blood flow to the penis, thereby causing a mild form of necrosis, and/or by damaging the nerves and tissue directly beneath the band by sheer force.
The reasoning and goals behind this activity are widely varied. It can be performed as part of a BDSM function, where a dominant would have their submissive 'band' in an effort to show their commitment or servitude. It can also be performed as a form of chastity or orgasm denial, where the goal is either to numb the penis, or damage it to such an extent that it can no longer become erect, thus rendering it useless. This provides a means to deter someone from having orgasms without dealing with Chastity Devices.
Penis banding can be done with a variety of materials. Ranging from a shoelace or rubber bands, to using actual elastrator bands that are used on animals for castration. Generally, the aforementioned elestrator bands are preferred for the act. An elastrator kit is also essential, as it allows the user to apply the bands, which cannot be stretched open easily. Tools to remove the band, such as cat claw clippers or safety scissors, are necessary also, as the bands are difficult to take off.
Banding has its risks: if bands are left on too long, blood clots could form, resulting in a stroke. There are risks of getting gangrene also. Banding is unpredictable, and those who take part in it must ensure that they not apply the bands for too long; the longer that the bands are in place, the higher the risk of blood clotting is. Those who band usually intend to cause penile numbness for a few days, but this can often last as long as a few weeks. It is recommended that bands are not applied for more than sixty minutes.
The state of the penis when banding is a critical aspect to the practicer's safety. It is unadvisable to perform banding on an erect penis, since the increased pressure from the bands could rupture penile tissues. This could lead to massive hemorrhaging and a trip to the hospital. However, banding while completely flaccid tends to result in more severe results, such as long term damage to nerves. Most practicants feel that being semi-flaccid is the preferred state.
The last key aspect of banding is how tight the bands are. Using a single elastrator band may produce nominal results in 30-40 minutes, compared to the significant results that using three bands together can cause within 3-5 minutes.