From the UL White Book:
"The clamps are marked with the following letters or combinations thereof to indicate that they are suitable for use with armored cable (‘‘A’’): flexible metal conduit – ‘‘F,’’ nonmetallic-sheathed cable – ‘‘N,’’ or flexible tubing (loom) – ‘‘T.’’ Clamps
suitable for Type MC metal-clad cable are marked ‘‘MCI’’ for metal-clad
interlocking armored cable, ‘‘MCI-A’’ for metal-clad interlocking armor
ground cable, ‘‘MCS’’ for metal-clad continuous smooth-sheath cable, and
‘‘MCC’’ for metal-clad continuous corrugated-sheath cable. If suitable for all
seven types, the clamp is marked ‘‘ALL.’’ Clamps suitable for nonmetallicsheathed
cable are also suitable for multiconductor underground feeder and
branch circuit cable where used in dry locations."
