Patent ID: 8186921

Claim:
A drain plug for an enclosure comprising a female-threaded opening, comprising: a male-threaded portion; a head portion comprising a drive structure and an annular groove formed on an under-head surface of the head portion and adjacent to the male-threaded portion wherein the groove has an inner boundary with a diameter less than an outer diameter of the male-threaded portion, the annular groove comprising a square cross section having a dimension of about 0.3 mm or more and 2.0 mm or less by about 1.0 mm or more and 10.0 mm or less, and an outer wall enclosing the annular groove; a washer of a square cross section in the groove, wherein the washer does not comprise an O-ring washer and comprises an elastic material selected from a group consisting of diene rubber, olefin rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, urethane rubber, and styrene rubber.