Single element print head

In a single print element head releasably attached to a drive shaft, the improvement wherein said print head comprises:

• a print head body having a central openind therethrough for receipt of the drive shaft and characters formed on the periphery thereof;
• a cap secured on said print head body around one end of said opening;
• a manual slide member held by said cap so as to be slidable in a perpendicular direction to the axis of the drive shaft, between a first and a second positions, said manual slide member having a cam means in the bottom portion thereof, said cam means consisting of a pair of cam surfaces which gradually diverge, from the mutually nearest portion towards the mutually farthest portion, each of said cam surfaces having a recess therein adjacent to its said farthest portion;
• and
• a spring disposed in a space formed between said cap and said body, said spring having a pair of arms adapted to move between an open position for releasing said print head body from the drive shaft and a closed position for fastening said print head body to the drive shaft, each of said arms having a free end contacting respectively with each of other cam surfaces each said free end being rested in a respective one of said recesses when said manual slide member is in said second position, said arms being moved from said open position to said closed position when said manual slide member is moved from said second position to said first position and wherein said spring is formed in a hair pin like shape and consists of a base portion and said pair of arms extending from said base portion, each of said arms being bent at its free end so as to be contacted with each of said cam surfaces respectively.