Patent ID: 7390137

Claim:
A writing instrument, comprising: a hollow case having an elongate axis, the case further comprising a first end; a first hole in the first end; a second end; a smooth outer surface; an inner surface; a second hole in the one side of the case; means for opening and re-closing the case; a switch mounted on the inner surface of one side of the case which communicates through the second hole with the outer surface of the case; the switch further comprising means for releasably engaging a cartridge within the case; means for operating the switch with one finger comprising a switch surface having a plurality of ridges arrayed substantially transversely to the elongate axis; and a cartridge within the case comprising a writing tip; the cartridge being releasably affixed to the means for engaging the cartridge, so that when the switch is in a first position, the writing tip extends from the first hole, and when the switch is in a second position, the writing tip is within the case; and at least the first end is flared into the shape of a torus, the center of the torus congruent to the center of said first hole, the central plane of the torus being perpendicular to the axis of said case; and the inner diameter of the torus is approximately equal to the diameter of said first hole, the outer diameter of the torus is approximately equal to three times the diameter of the first hole, and the thickness diameter of the torus is approximately equal to the diameter of the first hole.