Retractable writing implement

A writing implement comprising

• a. an elongate barrel having first and second openings at the opposite ends thereof,
• b. an elongate cap which includes an opening at one end thereof and which is rotatable with respect to said barrel,
• c. a ferrule which is removably received within said second opening of said barrel and which is in non-rotational frictional engagement with the inner sidewall surfaces of said barrel,
• d. a guide bushing which is non-rotatably affixed to said ferrule and which is received in said opening in said cap and about which said cap rotates, said guide bushing including an axially extending bore therein which is offset with respect to the longitudinal axis of said bushing,
• e. a retaining ring which is mounted for rotation on said guide bushing and which engages the inner surface of said cap so that said ring rotates with said cap,
• f. an elongate replaceable writing tube which extends through said bore in said bushing and which is adapted to move axially within said barrel, said writing tube including writing means at one end thereof,
• g. a cam member located within and affixed to said cap and including a helical cam surface which engages the other end of said writing tube,
• h. spring means for biasing said writing tube into engagement with said cam surface, so that, upon rotation of said cap in first direction, said cam surface causes the writing means of said writing tube to extend through said first opening in said barrel outwardly thereof and, upon rotation said cap in the opposite direction, said cam surface permits said writing means of said writing tube to be retracted within said barrel responsive to the urging of said spring means, said guide bushing being generally cylindrical in construction and extending beyond the end of the barrel to provide a surface about which said cap rotates, said bushing including a peripheral groove in which said retaining ring is received.