When looking at the M Series of Barrier Blocks from Curtis Industries the T suffix is calling out that the part is coming with brown market tabs mounted to the block. All of the other specifications would be the same. Here is a chart showing other suffixes and what they mean. For more information please consult the datasheet.
M Series parts with "T" suffix
MAT-1 MAT-2 MAT-3 MAT-4 MAT-5 MAT-6 MAT-7 MAT-8 MAT-9 MAT-10 MAT-11 MAT-12 MAT-13 MAT-14 MAT-15 MAT-16 MAT-17 MAT-18 MAT-19 MAT-20 MAT-22 MAT-21 MAT-23 MAT-24
MAT-1-ND MAT-2-ND MAT-3-ND MAT-4-ND MAT-5-ND MAT-6-ND MAT-7-ND MAT-8-ND MAT-9-ND MAT-10-ND MAT-11-ND MAT-12-ND MAT-13-ND MAT-14-ND MAT-15-ND MAT-16-ND MAT-17-ND MAT-18-ND MAT-19-ND MAT-20-ND MAT-22-ND MAT-21-ND MAT-23-ND MAT-24-ND