Abstract: A system for precision centering a bored rotary member upon a mounting shaft, which relatively loosely extends through the bore, includes a radially outwardly extending shoulder on the shaft against which one end of the bored member is seated. A generally triangular shaped, plate-like insert, having a central opening, is positioned over the other end of the bore. The corner portions of the insert are immovably fastened to the member and the shaft passes through the central opening. The periphery of the opening is defined by a series of spaced apart, equal radius, arcuate segments which form substantially line contacts with the shaft periphery. The radii of the segments are centered on the bore axis and are slightly shorter in length than the shaft radius, which is shorter than the bore radius. Thus, the arcuate segments resiliently compress radially inwardly around the shaft to center the bore upon the shaft.