Abstract: A writing instrument for thin lead refills comprising a housing and a lead feed mechanism located within the housing and wherein the feed of the lead refills is effected by a lead collet slidable axially against a spring force. The housing is sub-divided into front and rear housing sections which are axially adjacent one another and are relatively rotatable about a longitudinal axis of the instrument. To each housing section there is secured in rotation a component of a cam assembly comprising a thrust cam component and a thruster component. Upon relative rotation of the housing sections, the components interact with one another to slide the lead collet into projected open position for receiving a lead refill. One of the cam components is axially secured with the associated housing section and the other cam component is axially secured with the part of the lead feed mechanism carrying the lead collet and is axially displaceble with respect to the associated housing section.