Patent ID: 7011226

Claim:
A plug for a drain port in a container for holding a material, the plug comprising: a substantially flat plug plate body, of one chemical composition, adapted for mounting in said drain port and plugging said drain port when mounted therein, said plug plate body including opposite surfaces having a thickness L defined between the opposite surfaces from one of said opposite surfaces to the other of said opposite surfaces, and at least one groove having one of a rectangular shape, a substantially trapezoidal shape and a substantially V-shape and formed transversely in one of said opposite surfaces, the at least one groove having at least two different depths therein, one depth being a low strength portion where strength is decreased relative to the other depth of the groove by changing a groove thickness, which is defined from a groove bottom to the other of said opposite surfaces, the low strength portion being formed within a predetermined range from a center of said plug plate body, the groove having opposing walls extending from the groove bottom to a top of the groove at said one of said opposite surfaces in which the groove is formed, the groove having a width measured from one of said opposing walls to the other of said opposing walls in a direction parallel to one of said opposite surfaces, the width at the groove top being no less than the width at the groove bottom; wherein a thickness T 2 , defining a thinnest one of the groove thicknesses from the bottom of the groove to the other of said opposite surfaces in which the groove is formed, ranges from 0.05 mm to 0.7 mm, wherein the groove walls are disposed relative to one another at an angle θ measured from one opposing wall to the other of said opposing walls, the angle θ ranging from 0° to no more than 120°, and wherein a ratio (L/T 2 ) of the thickness L of said plug plate body to said thickness T 2 is equal to or more than 2.