Sizing Notation:

16-inch (8) is an 8-inch cable designed to make 16" circulars when combined with 4" interchangeable needle tips. 
20-inch (12) is a 12-inch cable designed to make 20" circulars when combined with 4" interchangeable needle tips.
24-inch (14) is a 14-inch cable designed to make 24" circulars when combined with 5" interchangeable needle tips.
32-inch (22) is a 22-inch cable designed to make 32" circulars when combined with 5" interchangeable needle tips.
40-inch (30) is a 30-inch cable designed to make 40" circulars when combined with 5" interchangeable needle tips.