Instruments which are in essence simply a string or strings and a string bearer. These instruments may have a resonator box, but removing it should not render the instrument unplayable (although it may result in quite a different sound being produced). They include the piano therefore, as well as other kinds of zithers such as the koto, and musical bows.

31 – Simple chordophones or zithers

311 – Bar or stick zithers – The string bearer is bar shaped.
311.1 Musical bows – The string bearer is flexible (and curved).
311.11 Idiochord musical bows – The string is cut from the bark of the cane, remaining attached at each end.
311.111 Mono-idiochord musical bows – Containing one string only
311.112 Poly-idiochord musical bows or harp-bows – Containing several strings that pass over some type of bridge.

311.12 Heterochord musical bows – The string is of separate material from the bearer.

311.121 Mono-heterochord musical bows – The bow has one heterochord string only.
311.121.1 Without resonator.
311.121.11 Without tuning noose.
311.121.12 With tuning noose.

311.121.2 With resonator.
311.121.21 With independent resonator.
311.121.22 With resonator attached.
311.121.221 Without tuning noose.
311.121.222 With tuning noose.

311.122    Poly-heterochord musical bows – The bow has several heterochord strings.
311.122.1 Without tuning noose.
311.122.2 With tuning noose.
311.2 Stick zithers – With rigid string carrier
311.21 Musical bow/stick – The string carrier has one rigid and one flexible end.

311.22 True stick zithers – NB Round sticks which happen to be hollow by chance do not belong on this account to the tube zithers, but are round-bar zithers; however, instruments in which a tubular cavity is employed as a true resonator, like the modern Mexican harpa, are tube zithers.

311.221 With one resonator gourd.
311.222 With several resonator gourds.

312 – Tube zithers – The string bearer is a vaulted surface.

312.1 Whole tube zithers – The string carrier is a complete tube.
312.11 Idiochord tube zithers.
312.12 Heterochord tube zithers.
312.121 Without extra resonator.
312.122 With extra resonator.

312.2 Half-tube zithers – The strings are stretched along the convex surface of a gutter.
312.21 Idiochord half-tube zithers.
312.22 Heterochord half-tube zithers.

313 – Raft zithers – The string bearer is composed of canes tied together in the manner of a raft

313.1 Idiochord raft zithers.
313.2 Heterochord raft zithers.

314 Board zithers – The string bearer is a board.

314.1 True board zithers.
314.11 Without resonator.
314.12 With resonator.
314.121 With resonator bowl.
314.122 With resonator box – the piano is part of this subdivision.

314.2 Board zither variations.
314.21 Ground zithers.
314.22 Harp zithers.

315 – Trough zithers – The strings are stretched across the mouth of a trough.

315.1 Without resonator.
315.2 With resonator.

316 – Frame zithers – The strings are stretched across an open frame.

316.1 Without resonator.
316.2 With resonator.