ergocockring

A cock ring or cockring is a ring worn around the penis, usually at the base. The primary purpose of wearing a cock ring is to restrict the flow of blood from the erect penis in order to produce a stronger erection or to maintain an erection for a longer period of time. Genital adornment is another purpose, as is repositioning the genitals to provide an enhanced appearance.

imeasurements:

cr6.stl - 50mm diameter. (This is the one I use the most)
cr4.stl - 45mm diameter.

use at your own risk.