Ball point pen with two cartridges

A writing instrument in the form of a ball-point pen having two ink cartridges which, through turning of the shaft, can be alternately brought into writing position, said writing instrument comprising means defining a space provided at the rear of the shaft to accommodate stamping mechanisms, in combination with

• (a) a longitudinally extending barrel forming the shaft of said ballpoint pen;
• (b) a longitudinally extending guide tube mounted within said barrel, said guide tube having two oppositely disposed lateral, longitudinally extending slots and two oppositely disposed lateral, longitudinally extending rails, said slots and said rails being displaced from one another.
• (c) a pair of slides slidably mounted in said guide tube to be moved towards and away from the writing position, each slide consisting of a semicylindrical segment having a nose thereon extending into one of said slots of said guide tube, a pair of recesses engaging said rails of said guide tube, and an extension on the writing position side on which a tube is mounted surrounded by a coil spring biasing said slide away from the writing position onto which tube an ink cartridge is mounted;
• and
• (d) a generally tubular switching casing rotatably surrounding said guide tube, said switching casing having downwardly facing curved switching cam surfaces engaging a portion of each of said slides, said cam surfaces including a first portion engaging one of said slides when said slide is in a retracted position and a second portion engaging said other slide when said other slide is in the writing position, so that rotation of said casing causes said first portion of said cam surfaces to move the respective slide downwardly against said biasing means into the writing position as said second portion of said cam surfaces allows said other slide to move upwardly away from the writing position, said switching casing further having a bore alignable with a bore in a protective sleeve surrounding said casing and a holder for the attachment of an accessory device;
• wherein said switching casing is a tube and the curved switching cam surface of said switching casing is formed by sectioning said casing at an angle inclined relative to a longitudinal axis thereof, said switching cam surface having a V-shaped notch at an apex thereof for arresting said nose of each of said slides.