THE PRIMARY use ofa rolling pin is to turn a ball of pastry dough into a thin, even, flat disc without tearing it or making it tough. I have seen James Beard do this without a pin, using only the tips of his fingers. I have seen Jacques Pepin do it with a wine bottle. But for most people who bake, a good rolling pin is a necessity.

Rolling pins come either with moving parts or as a single piece of wood. The classis American Rolling Pin is in the first category, made of a wooden cylinder, two handles and a system of ball bearings that allows the cylinder to turn freely. The best American pins are heavy, the theory being that the weight will do most of the work so the baker will not be forced to push down on the dough, thereby reducing the possibility of tearing it.

The smooth, steady rolling action of the ball bearings will produce a flat and even sheet of pastry. The finest American-style pins are made by the Thorpe Rolling Pin Company of Cheshire, Conn. They come in 10 1/2-, 15- and 18-inch models with a ball-bearing system that does not require lubrication. The 15-inch pin, made of lacquered and polished hardwood, is the most convenient size for normal home use. It has a 3 1/2-inch diameter for a nice full turn, weighs 4 1/2 pounds and generally retails for about $18.50.

The second style of rolling pin with moving parts is called a Tutove. The pin looks somewhat like the classic American design, but the surface of the plastic cylinder is covered with a series of 1 3/8-inch grooves that run the entire length of the pin from end to end. It is used in making puff paste, a crisp, flaky pastry made up of dozens of layers of dough. The grooves in the Tutove help distribute the butter evenly between the layers of dough. An exemplary Tutove rolling pin is imported by Cuisinart at $65.

The standard in one-piece rolling pins is the Straight French Pin: a perfect cylinder made of hardwood with a length of approximately 18 inches and a diameter of about 2 inches. Most European pastry chefs prefer this style, claiming a better "feel." The transfer of pressure from the hands directly to the pin and then to the pastry affords a more sensitive touch. Good quality straight pins cost about $4.

The tapered rolling pin is thicker in the center and thinner at the ends, and requires a special effort to give an even thickness to the dough. I do not recommend tapered pins for general use. But at $3.50 they are ideal for making pizza, lahma bi ajeen or any other circular dough that ends up as a "plate" for a sauce or filling. The tapered shape will result in a disc of dough with a trough in the center and a thick ridge on the edges.

Virtually every cuisine has its own special rolling pin, often available in the small shops that specialize in the ingredients and equipment of a particular nation. There is a Syrian Pin that has the general shape of an American roller, made of a single block of apricot wood. It is used to make meat pies.

There is a short, narrow Chinese Pin that looks very much like the straight, classic French roller and is used for making the pancakes that go with Peking Duck, as well as the wrappers for wonton. The Scandinavians have a knobbed rolling pin covered with rows of tiny pyramids that leave the characteristic holes found in rye-flour flatbreads.

There is a small, tapered Indian pin for making pooris. The longest styles are the Italian Pins for making pasta.

There is an entire range of rolling pins that are purely cosmetic in function.The Rotterdam Roller decorates cakes and cookies with a basketweave pattern. The Springerle Rolling Pin produces 16 different birds, flowers and fruit designs for the anise-flavored Christmas cookies of Switzerland and Germany, called Springerle.

Whichever rolling pins you purchase, always select a smooth-finished, hard material that will reject fats and moisture. Look down the length of the pin like a pool shark checking a cue stick, and make sure it is not warped or uneven. Place the center of the pin on the top of a bottle to test its balance. If it's not perfect, reject it. Also, bypass the elegant but easily broken porcelain pins, as well as the glass pins that suggest you fill them with ice to keep the cylinder cool - they will sweat and destroy your pastry. The simple, straight French pin is probably the best all-purpose roller, and the least expensive.