It usually takes the Sugar Maple more than 40 years to grow larger than 12 inches in diameter at chest height. At that time, it is ready for one tap. Near the end of February, when alternating freezing and thawing temperatures generally begin, sugarmakers make the rounds of their "sugarwoods", drilling 1 cm (7/16") holes about 5 cm (2-2 1/2") into the trunk of the tree. Depending on the tree's diameter and strength, it may be fitted with as many as three (3) taps. Trees with trunks less than 25 cm in diameter should not be tapped at all. Prudent tapping is harmless to the maple - many trees have been tapped continuously for more than 150 years. Metal or plastic spouts are inserted, and buckets are hung, or plastic tubing is connected from tree to tree. From mid-march to the beginning of April, alternate freezing and thawing changes the pressure inside the tree and starts the sap flowing with the weather growing warmer, and temperatures rising above the freezing level. At this point, the clear, slightly sweet liquid will begin to drip into the buckets or through the network of tubing. Traditionally, after the sap was collected in troughs, it was emptied into a large barrel carried on a horse-driven sleigh. In the mid-1970's, this technique was gradually replaced by a tubing system, in which a partial vacuum is maintained using a pump. This method of collection, which does not damage the trees, yields more sap and reduces the manpower required and allows the producer to tap more trees, including those located in rugged terrain. When a pipeline system is used, the sap flows directly downhill through the tubing to a central collection point. The sap will stop "running" when temperatures fall below freezing, and run again when it rises. It is a general rule-of-thumb that each tap will yield 10 gallons of sap throughout an approximate six week season, producing 1 quart of maple syrup. In several maple sugaring operations, the maple syrup production process is the same, but the equipment has changed. Taps, or spigots, are made of metal. Buckets are aluminum or plastic. Buckets have lids to keep the sap clean, free from snow, bark, and twigs. Sap is gathered by walking from tree to tree only in traditional Sugar Bushes. In modern, more efficient Sugar Bushes, elaborate tree-to-tree pipe systems are used to run the sap directly into the Sugar Camp.