Abstract: A synthetic resin pen unit has a cylindrical outer annular member with inwardly extending bent and straight members. Each bent member has a base portion extending from the inner wall so that it is inclined with respect to a phantom line connecting the base of the bent member to the central axis of the cylindrical member. Ink grooves are formed between the inwardly extending members. The flexibility of the pan unit is a function of the percentage of bent members so that by proper selection and arrangement the pen characteristics can be optimized.