Abstract: The present invention is directed to a floating cap or spacer and centrifuge tube assembly which provide adequate resistance to the deforming forces exerted on it. The exterior wall of the tube stem is provided with an annular ridge and the support spacer is provided with an annular groove which mates with the ridge on the tube stem to form an interlocking coupling.

Abstract: The present invention directed to a plug for sealing a centrifuge tube. The plug of the present invention is shaped and sized to provide an interference fit between the plug and the tube stem of the centrifuge tube. In the described embodiment, the plug is configured with a tapered body narrowing to a flared end. To facilitate the insertion and removal of the plug with moderate force, without compromising the restraining capability of the interference fit, the area of interference contact between the flared end and the filler stem is strategically reduced. An o-ring is provided in a annular groove around the tapered body. The flared end creates an interference fit with a tapered filler stem, whereby the plug is secured in the filler stem with a snapping action when the flared end of the plug extends into the tube beyond the tapered filler stem.