between the receptacle and the one holder is broken application_number US 50868383 A description the invention will be described herein in terms of a device for exchanging writing instruments such as may be used in the conventional flat bed plotter 1 shown in fig1 which has a bar 2 that can be moved back and forth in one direction over the drawing surface 3 and a holder 5 secured to bar 2 by means of a drawing head not shown the drawing head is movable back and forth on the bar 2 in the longitudinal direction thereof in the conventional manner magazines 4 for writing instruments are also present on the stationary frame of the plotter 1 and are shown in a highly simplified and schematic manner holders not shown but corresponding to the holder 5 are secured in these instrument magazines 4 two holders 5 5 39 of identical design are shown in fig2 each in the approximate shape of half a cylindrical shell the holders facing one another with their open sides the various parts of the two holders are identified with the same reference numerals but those of one holder which will later be assumed to be the stationary holder are marked with a prime 39 because the design of the two holders is the same it will be sufficient to describe only one holder in detail the holder 5 which by way of example is of plastic or non ferromagnetic metal has two permanent magnets 6 7 on its inner face located opposite the open side the permanent magnets 6 7 are located on a straight line extending parallel to the longitudinal axis and are spaced apart axially from one.