The piccolo clarinets are members of the clarinet family, smaller an higher pitched than the more familiar high soprano clarinets in E♭ and D. None is common, but the most often used piccolo clarinet is the A♭ clarinet, sounding nearly an octave higher than the B♭ clarinet. Shackleton also lists obsolete instruments in C, B♭, and A♮. Some writers call these sopranino clarinets or octave clarinets. The boundary between the piccolo and soprano clarinets is not well-defined, and the rare instruments in G and F might be considered as either. Shackleton uses it to refer to the E♭ and D clarinets, as well as obsolete instruments in G, F, and E, but this classification, while useful, seems to be uncommon; the E♭ and D instruments are more usually considered soprano clarinets.