Cluck Cluck Sew CCS192 Diagonal Seam Guide Tape, 1 Roll 5/8" Wide by 10 Yards
Each roll 5/8" wide tape and is 10 yards. The black lines on each side of the red seam line replicate a perfect 1/4" seam, so getting a perfect 1/4", lining up fabric, or even making half square triangles is easy.