The ball point pen comprises an elongate, hollow barrel (10), a tubular element (12) arranged coaxially within the upper portion of the barrel (10), a writing point (18) and a push-button (22) arranged to control the extension/withdrawal of the writing point (18) relative to the barrel (10). At least one longitudinal rib (40) and an annular projection (42) are formed either on the inner surface of the sleeve (24) of the push-button (22) or on the outer surface of the tubular element (12) and, correspondingly, at least one raised, shaped element (44) is formed either on the outer surface of the tubular element (12) or on the inner surface of the sleeve (24) so as to interfere radially with the annular projection (42) and to define at least one longitudinal groove (46) adapted to form a seat for the rib (40) when the sleeve (24) is fitted onto the tubular element (12). IMAGE
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