The recorder is a family of woodwind musical instruments in the group known as internal duct flutes: flutes with a whistle mouthpiece, also known as fipple flutes. A recorder can be distinguished from other duct flutes by the presence of a thumb-hole for the upper hand and seven finger-holes: three for the upper hand and four for the lower. It is the most prominent duct flute in the western classical tradition. Recorders are made in various sizes with names and compasses roughly corresponding to various vocal ranges. The sizes most commonly in use today are the soprano (also known as descant, lowest note C5), alto (also known as treble, lowest note F4), tenor (lowest note C4), and bass (lowest note F3). Recorders were traditionally constructed from wood or ivory. Modern professional instruments are almost invariably of wood, often boxwood; student and scholastic recorders are commonly of moulded plastic. The recorders' internal and external proportions vary, but the bore is generally reverse conical (i.e. tapering towards the foot) to cylindrical, and all recorder fingering systems make extensive use of forked fingerings.