A device (100), for the checking and measurement of the journal bearing clearance between the outer bearing on the rudder shaft (25) of a rudder for water-borne craft and the inner bearing (32) on the rudder trunk (20) corresponding with the outer bearing (31), is characterised by a measurement rail (70) made of a springy elastic material having internal stiffness, which can be introduced by means of a guide rail (60), provided with a grip-type handle (61), into the gap between the outer bearing and the inner bearing and hence into the clearance measurement region, with a measurement probe (80) located at its free end (70a) for the clearance width measurement, wherein the measurement rail (70) with the measurement probe (80) with a prescribed thickness (a) are exchanged for measurement rails with measurement probes with other thicknesses until the achievement of an agreement of the clearance width with the thickness of a measurement rail (70) with the measurement probe (80).