the schematic representation in fig1 shows a one - piece probe pin carrier 1 , which is divided into a lower part 2 , a flange 3 with parallel surfaces 4 , 5 and a cylinder 6 . threaded sockets or jack sockets 7a - 7e are provided in the lower part 2 to accommodate probe pins or probe pin combinations , not represented here . balls 8 , 9 and 10 are set into the surface 5 , facing the cylinder 6 , of the flange 3 at the same distance from the axis of the probe pin carrier 1 and staggered by 120 ° to one another . in addition , the flange 3 is provided , on its outer periphery , with a groove 3a , which , however , can be replaced by a bore hole . the function of the balls 8 - 10 and the groove 3a or the bore hole will be described further below . referring to fig4 a slot ( 48 ) is provided at the free end of the cylinder 6 parallel to the axis of the latter . a cylinder pin 11 , the function of which will also be described further below , is mounted perpendicular to the slot . a probe pin change device , which is attached to a probe head , not represented , of a coordinate instrument , is shown schematically in the representation of fig2 . a flat recess ( 14 ), with slightly conical inner surfaces 15 and a planar base surface 16 , and a bore hole 17 are provided in the lower part of the housing 13 . an orientation pin 18 is set into the base surface ( 16 ) parallel to the axis of symmetry of the housing 13 . in addition , referring to fig3 pairs of rollers 19 - 21 , the function of which is described further below , are provided on the base surface 16 staggered at 120 ° to one another . a deep recess 22 is provided in the upper part of the housing 13 . a base , which is penetrated by the bore hole 17 , is created between this recess and the flat recess 14 . the deep recess 22 accommodates a rocker lever clamp mechanism 23 which comprises a lever 24 of the u - shaped construction and a flat lever 25 which is provided with a coupling part 26 . the side walls of the u - shaped lever 24 are each provided , at the lower end 24a , with a mounting bore hole 27 , 28 into which pins 29 , 30 engage , which are fixed in the housing 13 about which the u - shaped lever ( 24 ) is mounted so that it can pivot . the coupling part 26 has a groove , open on one side , that has conically converging edges . alternatively , the edges can be parallel to each other . a further mounting bore hole 32 , 33 is provided at the upper end 31 of each of the side walls of the u - shaped lever . these accommodate a pin 34 which bears the flat lever 25 which is pivotable about the pin . the probe pin change device or mount , provided in the probe head , has a mechanical clamp mechanism which acts on the bearing part of the probe pin carrier , and compression - creating or tension - creating media , which actuate the clamp mechanism . a spring housing 35 is fixed on the left of the central region of the housing 13 and a cylinder pot 36 , which accommodates a hydraulic cylinder or pneumatic cylinder 37 with piston 38 , is fixed to the right of the central region of the housing 13 , aligned with the axis of the spring housing 35 . a push rod 39 of a slider 40 , which , passing through an aperture 41 in the rear wall of the u - shaped lever 24 , grasps the flat lever 25 , is guided with lateral play in the piston 38 . the flat lever 25 is connected positively but in an articulated manner with the slider 40 by means of a connecting pin 42 . the end of the slider 40 which projects beyond the flat lever 25 serves as support for a compression spring 43 , which is mounted in the spring housing 35 . a tension spring 44 is fixed with one end to the u - shaped lever 24 , and with the other end is hooked to a retaining bolt 45 which , together with a stop 46 , is mounted in an eccentric extension 47 of the deep recess 22 in the housing 13 . the mount described hitherto can thus apply the necessary clamp force for retention of the probe pin carrier 1 by spring force or by compressed air . in the present case , the compression spring 43 serves for clamping . on failure of the compressed air , the clamp force , which is generated by the compression spring 43 , is maintained . to insert the probe pin carrier 1 , an &# 34 ; opening &# 34 ; procedure is carried out . the &# 34 ; opening &# 34 ; procedure is initiated by feeding compressed air through an aperture 36a to the pressure cylinder 37 . the piston 38 is thereby pushed to the left and transfers the movement , via the push rod 39 and the slider 40 , to the rocker lever clamp mechanism 23 . both lever 24 and flat lever 25 pivot together initially to the left about the pins 29 , 30 until a stop surface of the u - shaped lever 24 comes into contact with the stop 46 . this effective pivotting of flat lever 25 about pins 29 , 30 causes a slight downward movement of coupling part 26 , as can be seen from fig2 since the pivot axis 29 , 30 is essentially at the right - hand end of the engagement surface of the coupling part 26 . on further application of pressure , the flat lever 25 then pivots about the pin 34 against the force of the compression spring 43 until it comes to rest on the housing wall . this pivotting about pin 34 causes a lateral movement of coupling part 26 . the probe pin carrier 1 can now be introduced into the change device . during this insertion , the probe pin carrier 1 is pre - oriented coarsely by the slightly conical inner surfaces 15 of the flat recess 14 in the lower part of the housing 13 and by the orientation pin 18 , set into the base surface 16 , and the groove or bore hole 3a in the flange 3 of the probe pin carrier 1 . on release of the pneumatically or hydraulically generated pressure , the lever 24 initially remains in its position under the influence of the tension spring 44 , while the lever 25 pivots about the pin 34 and laterally moves the coupling part 26 , of hook - shaped design , into engagement with the pin 11 of the probe pin carrier 1 . the rocker lever clamp mechanism ( i . e ., both lever 24 and flat lever 25 ) then pivots about the shaft 29 , 30 and locks the probe pin carrier in the three - point bearing as a result of the slight upward movement of coupling part 26 . the positive coupling between probe pin carrier and probe head thereby prevents release of the carrier from the probe head if the carrier is overstressed on collision . to change the probe pin carrier , the &# 34 ; opening38 procedure is carried out . the carrier can then be removed and set down on an appropriate depository .