Abstract: A capping mechanism comprising an active feeder (20) device in which caps (1, 10) are fed actively forward arranged top-to-bottom along a feeding axis (30), and a hollow rotatable and linearly movable chuck device (40) arranged at the feeder's outlet end (22) and devised to grip a cap and mount said cap to a container opening. The feeder device preferably comprises movable members working in pairs (23, 24 and 25, 26 resp.) alternating to influence a row or pile of caps.