Wikipedia
Comb binding
Spine capacity
Inches
Millimeters
Sheets of paper
3/16"
4 mm
16
1/4"
6 mm
25
5/16"
8 mm
40
3/8"
10 mm
55
7/16"
11 mm
70
1/2"
12 mm
85
9/16"
14 mm
100
5/8"
16 mm
125
3/4"
20 mm
150
7/8"
22 mm
175
1"
25 mm
200
1⅛"
28 mm
250
1¼"
32 mm
275
1½"
38 mm
325
1¾"
45 mm
375
2"
51 mm
425
Comb binding (sometimes referred to as "cerlox or surelox binding") is one of many ways to bind pages together into a book. This method uses round plastic spines with 19 rings (for US Letter size) or 21 rings (for A4 size) and a hole puncher that makes rectangular holes. Comb binding is sometimes referred to as plastic comb binding or spiral comb binding.