This paper presents a novel constant force mechanism based on a 11- revolute joints spatial linkage using simple pin joints and two regular springs. Passive linear sliders with ball bearings are not suitable for certain applications such as in medical environment or for miniaturization. Using only revolute joints in the mechanism allows for replacing all ball bearings with PTFE pin joints, which can be made smaller than ball bearings and are bio-compatible. Pin joints however have the disadvantage of generating friction, which can affect the quality of the constant force at the output link. This paper introduces the new pin joints constant force mechanism and presents an analysis of the effect of the friction generated by the joints on the output force.