Baseball bats have evolved along with the sport of baseball, changing over the decades from the simple and varied wooden sticks of the late 1800s to the modern bats used in Major League Baseball today. The rules of the game govern the materials, form and, in particular, the dimensions of a regulation baseball bat. To be approved for regulation play, each bat must meet these critical measurement standards.
In 1859, the first rule was introduced concerning the diameter of a bat. The rule stated that a bat could be no larger than 2 1/2 inches in diameter. Eventually, other rulings changed the maximum diameter to 2 3/4 inches. As of 2010, maximum diameter of a Major League Baseball bat was set to 2.61 inches.
In 1869, another rule set the maximum length of a regulation baseball bat to no more than 42 inches. This rule continues to this day in Major League Baseball.
The MLB rules also state that the handle of the bat can be covered with any substance or material, such as pine tar, that improves the grip of the bat for up to 18 inches from the end of the handle. If any substance or material extends beyond that measure, the bat will be removed from sanctioned play.
Some wooden baseball bats have a cupped impression on the end of the bat barrel. The cup must be no deeper that 1 inch and no wider that 2 inches and cannot have any right angles. There can be no foreign substances within the cup.
According to the rules of Major League Baseball, a bat must be a round stick made of solid wood with a smooth surface. No laminated or experimental bats are allowed without approval from the Rules Committee. Bats that are colored in any way must first be approved by the Rules Committee.