Cap nut for envelopment casting, casting including the cap nut and method of enveloping the cap nut in casting

A casting comprising:

• a cast portion made of casting material, the cast portion having an outer peripheral surface;
• and
• a cap nut enveloped in the cast portion, the cap nut including:
• a substantially cylindrical body having a first end and a second end, the body having a hole and an outer peripheral surface to be enveloped in the casting material, the body having an exposed surface adjacent to the hole at the first end thereof, the exposed surface being exposed to an outside of the casting, the body having formed in the outer peripheral surface thereof a tapered surface that broadens from the second end of the body toward the first end, the body having formed in the tapered surface a retaining means for preventing the cap nut from falling off from the casting, wherein the body is installable in and removable from a pattern for forming a sand mold at the tapered surface;
• and
• a cylindrical extension protruding from the exposed surface of the body for being buried in the sand mold, the hole extending through the extension, the cap nut having formed therearound between the body and the extension a circumferential notch having substantially a V-shaped cross-section.