Throwaway closure for test tube

Claim 1

A. In combination with a cylindrical glass test tube having a smooth cylindrical interior wall, a molded plastic closure for said test tube, b. said closure having a cylindrical wall portion of slightly larger interior diameter than the external diameter of the test tube, sufficient to provide a loose fit, c. and a substantially circular flat top portion at right angles to said wall portion and closing one end thereof, d. an integral annular internal plug portion projecting downwardly from said top portion and concentric with said top portion and of a size to fit snugly and airtightly within said tube when the closure is applied to the open end thereof, by engagement with said smooth cylindrical wall portion, e. said plug portion having a first section comprising an external conical wall surface increasing outwardly in diameter at an angle in the order of 10* from the vertical for a short distance from its junction with said top portion, to a maximum transverse diameter, f. said plug portion having a second section comprising an external conical wall surface decreasing from said maximum diameter to a minimum diameter at an angle in the order of 30* to the vertical to provide a reversely tapering tip portion facilitating entry of the plug portion into a test tube, g. said cylindrical wall portion of the closure being of sufficiently greater axial length than the plug portion to prevent any substantial degree of cocking of the plug portion.