Japanese residential threshold comes in two sizes: 0.7 inch (18 mm) wide and 0.8 inch (21 mm) wide. This is a multi-purpose door sliding tape that can be used in both 0.7 inch (18 mm) and 0.8 inch (21 mm) widths by breaking the tape.
If the threshold is 21mm wide, please use it as is. If the width is 0.7 inches (18 mm), please trim the tape along the notch. Since it is a multi-purpose model, you can use it without checking the width of the threshold in your home.