| http://www.w3.org/ns/prov#value | - The apparatus described in claim l and in which each of the clamping jaws extends between convolutions of the spiral of its cushion rearward of the axis of the spiral whereby most of the resilience of the cushion is in front of the clamp jaw, and the means for holding the jaws is a screw that is adjustable to change gradually the pressure of the cushion against the test tube or the like. 3.
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