Abstract: A barrier, installed in the sewage pipe and intended to prevent the penetration of rats, that comprises a main body shaped like a short hollow sleeve, a main obstructing plate, a secondary obstructing plate, a first locking tongue, and a second locking tongue; whereby the sleeve is shaped like a short hollow pipe with a flat top part; and whereby the main obstructing plate is shaped like an ellipse whose upper edge is truncated, forming a straight line, and which has a hole at the bottom beneath which are two protruding pins. A top pin and a bottom pin; and whereby the secondary obstructing plate is also shaped like an ellipse with a truncated upper edge, forming a straight line, and has a protruding pin near its bottom edge; and whereby the first and second locking tongues have the general shape of a rectangle; and whereby the main obstructing plate, the secondary obstructing plate, and the locking tongues are all attached to the flat top of the sleeve, from the inside, using hinges.

Abstract: A grinding tool includes a rotary motor driving a rotary drive shaft, a first grinding disc having a center opening for receiving the drive shaft, with the outer end of the drive shaft projecting through the opening in the grinding disk, a spacer assembly having a socket at one end receiving the projecting end of the drive shaft, a pin at the opposite end, and a spacer between said socket and pin, a second grinding disc having a center opening for receiving the pin of the spacer assembly with the outer end of the pin projecting through the latter opening and an outer collar attached to the projecting end of the pin for securing the two grinding discs to the drive shaft in spaced-apart relationship such as to enable the grinding tool to simultaneously cut two spaced grooves.