An assembly of hardware that (a) is arranged so that a number of circuits, usually of the same or similar type, such as fiber optic circuits or electronic circuits, appear on jacks for monitoring, interconnecting, and testing purposes, (b) is used at many locations, such as technical control facilities, patch-and-test facilities, and central offices (COs), such as telephone exchanges and switching centers, and (c) is often used for special purposes, such as direct-current (dc), voice-frequency (VF), group, coaxial-cable, equal-level, and digital-data electronic and fiber optic circuits. See  coaxial patch bay,  digital circuit patch bay,  digital primary patch bay,  direct-current patch bay,  D-patch bay,  equal-level patch bay,  group patch bay,  K-patch bay,  MM-patch bay,  M-patch bay,  voice-frequency primary patch bay. See also  central office,  circuit,  coaxial cable,  direct current,  electronic,  electronic circuit,  fiber optic circuit,  group,  interposition trunk,  jack,  jack field,  level,  patch,  patch-and-test facility,  patch panel,  secure voice cord board,  switching center,  telephone exchange,  test,  voice frequency.