Further to what ‘tankbarrel’ posted. If there are 2 digits for the diameter/dimension of the cord or propellant grain, then divide by 100 to get the diameter in inches. If there are 3 digits then divide by 1,000.
So W. T. 144-048 means:
W = 'Cordite W' = a type of solvent process-produced cordite that uses the stabiliser and gelatiniser carbamite (symmetrical diethyldiphenyl urea) & not mineral jelly, formerly known as R.D.H./A., the W is in reference to Waltham Abbey where is was developed;
T = Tubular cord;
144 = external diameter in inches divided by 1,000 = 0.144”(3.66 mm);
048 = internal diameter in inches divided by 1,000 = 0.048” (1.22 mm).
You may also see propellant referred to by a 'Size xx' or 'Size xxx'. As before divide by 100 or 1,000 depending on the number of digits.
For example Size 12, and Size 320. For the former its external diameter is 0.12" and for the latter 0.32".
Please note that Sizes 1-9 are divided by 100.