Abstract: A tool for installing oil or grease seals. The tool includes a cup member with a driving handle at the top thereof. Various sizes of a seal installing member are provided and all have the same upper cylindrical portion with the lower cylindrical portion being of various sizes, depending on the seal with which it is to be used. The tool also includes a pair of extension sleeves, one with an internal rib and the other with an external rib for supporting the cylindrical portions of the sleeve and the installing part when assembled. Each of the second parts and the sleeves include locking pins or slots for receiving the locking pins. The working portion of the tool is the lower annular end face and the cup-like top portion includes a closed face on the top for supporting the tool or one of the extension sleeves.