3B

3B or 3-B may refer to:
 * Third baseman
 * Triple (baseball)
 * 3B Computers, a range of computers produced by AT&T during the 1980s
 * 3B Junior, a department of the Japanese entertainment company Stardust Promotion
 * 3B Lab, a Japanese popular music group
 * Three Bs, a designation for three well-known classical composers
 * 3B, a very soft grade of pencil lead

 may refer to: