The puck for a sample tube includes a housing, a spring device and an end cap. The spring device has an annular base portion and angularly spaced spring arms that extend upwardly from the base portion and then bend downwardly toward the base portion. The end cap includes a hub portion around which the spring device is mounted. The cap with the spring device are fixed at one end of the housing and a portion of the spring arms extend into the interior space of the housing. The downwardly directed portion of the spring arm includes a sample tube engaging portion that is substantially parallel with a central axis of the housing. Thus a sample tube inserted in the puck engages the sample tube engaging portions of the spring arms which exert a biasing force against the sample tube. The spring arms provide an optimum restraining force against the sample tube to permit easy insertion and removal of the sample tube from the puck.