Does anybody know what the letters "N" and "T" indicate on Romex clamps with metal boxes? The N is on one side and the T is on the other. I don't think it has anything to do with the manufacturer because I have seen this on several different brands. It's just one of those things that I have always wondered.

nob & tube

I'm not one who could bag on spelling... Isn't it Knob & Tube? Nob is a town in Isreal.

Otherwise, I have no idea.

The mark is to show what the clamp is listed for. I'm sure the N is for NM cable. Don't know about the T.
Stop at the supply house and look at their box catalogue it will have all the clamps listed. That is where I had to go last time to check on AC cable clamps.

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."

Thank You.
Alan--