Epson TM-C3500 Series Technical Reference Manual page 206

Continuous paper (Blackmark)
<Back side>
Center of black marks
Center of paper width
Perforation position
0.5 mm or more
(When using fanfold
paper)
Media type
Media source
Paper width
Black mark width
Black mark length
Center of a black mark
Gaps between black marks
Paper thickness
Paper core
External diameter
Winding direction
Do not use the paper with a hole or cutout.
206
Black mark width
Plain / Matte
Roll paper
30 to 108 mm {1.18 to 4.25"}
13 mm {0.51"} or more
4 mm {0.16"} or more
(with a width of at least 4 mm around)
8.5 mm  1 mm {0.33  0.039"}
8 to 1117.6 mm {0.32 to 44"}
0.084 to 0.124 mm {0.003 to 0.004"}
External diameter: 44.1 mm {1.74"} or more
Maximum 101.6 mm {4"}
Printing face must be facing outside.
<Printing side>
Center of paper
width
Paper feeding
direction
Black mark
receipt