Here is how to read the Marks on a Railcar:
LT-WT: This is the unloaded weaght in multiples of 100 pounds or kilograms. cars are weighed when new and reweighed periodically thereafter, or when repairs or modifications change the weight Make note: look for NEW: this will be followed by 2 numbers the month and last 2 numbers of the date.
LD LMT: Maximum permissible weight of contents, including the lading its self counting the load, and temp fixtures as well. The load limit is determined by subtracting the light weight from the total weight.
Capacity (CAPY)is normal weight of lading the car is rated for, in mulyiples of 1,000 pounds.
The new date: (NEW): indicates when the car was weighed new / or re-weighed to find its light weight
BLT: Build Date.
Plate C is an ARR (Association of American Railroads) diagram that outlines the maximum size a car can be for clearance on most railroad lines. A car that exceeds these dimensions must be stenciled "Exceeds Plate C", and thus would be restricted from general interchange service becouse it might not clear certian bridges or outher structures on some roads. Outher Plates that I Know of or have seen: A,B,C,D,E, and F.
Tank Cars: in general tell there capacity in gallons in which they hold.