Abstract: A test tube holder for holding a test tube having an upper lip, includes a holder ring having an opening therein through which the test tube can be inserted; and a lock down clamp secured to the holder and including a lock down member movable over the holder and over the upper lip of the test tube, a moving assembly connected between the lock down member and the holder for moving the lock down member between a locking position in blocking relation to movement of the test tube out of the holder, and a release position out of the blocking relation, the moving assembly including a lever arm pivotally connected to the holder, the lock down member being fixed to an upper end of the lever arm, a pivoting assembly connected with the holder and to which the lever arm is pivotally connected, and a locking assembly connected with the moving assembly for releasably maintaining the lock down member in the locking position, the locking assembly including a ridge roll member secured to the lever arm, and a ridge on the hol