The spacebands that I have here at the shop are 4 lines. I assumed that the number of identifying lines marked in the side of the spaceband correspond with the thickness of the space. Nope. I was wrong. The breakdown is below. Info from "Linotype Keyboard Operation" book.
One Line: Thick
For Normal spacing of medium size faces where close spacing is not required.
Two Lines: Extra Thin
For close spacing. Recommended for offices doing good book and job work and those using small faces.
Three Lines: Extra Thick
Used only for large display faces where wide spacing is required.
Four Lines: Special Taper
Similar to the wide range (see below) but a little thicker at both minimum and maximum points.
Five Lines: Wide Range
Gives extreme flexibility of spacing. Thin enough for close spacing, with ample range of expansion for wide spacing.