This little feller is a "German Spermatorrhoea Ring," ca 1894. Spermatorrhoea ("involuntary loss of semen") was best fought with this toothy beast, which also doubled as a cure for Onanism ("voluntary discharges from masturbation").
An extremely rare Spermatorrhoea ring fastened with a screw. With provenance from the original German catalogue dating from 1894. Spermatorrhoea means involuntary loss of semen, although the rings were also intended to prevent voluntary discharges from masturbation or Onanism (Originating from Onan who originally "spilt his seed on the ground" Genesis 38:7-9). The ring was placed at the base of the penis and fasted with a screw such that any engorgement of the organ would meet with the teeth of the ring and arrest the process.
German Spermatorrhoea Ring (screw catch)
(via JWZ)