Drop in curling, Bill Collier Ice Arena, Running Y Ranch, Klamath Falls, Oregon.
The curling stone, (also sometimes rock, North America) as defined by the World Curling Federation is a thick stone disc weighing between 38 and 44 pounds (17 and 20 kg) with a handle attached to the top. The maximum allowable circumference is 36 inches (910 mm). The minimum height is 4.5 inches (110 mm). The handle is attached by a bolt running vertically through a hole in the centre of the stone. The handle allows the stone to be gripped and rotated upon release; on properly prepared ice, the stone's path will bend (curl) in the direction the front edge of the stone is turning, especially as the stone slows. The handles are coloured to identify the stones by team. Two popular colours in major tournaments are red and yellow. The only part of the stone in contact with the ice is the running surface, a narrow, flat annulus or ring, 0.25 to 0.50 inch (6.3 to 13 mm) wide and about 5 inches (130 mm) in diameter; the sides of the stone bulge convex down to the ring and the inside of the ring is hollowed concave to clear the ice.