Four-String Version of Bertram Binder
This 4-string version of the binder produces a near even force on the blank since the clockwise windings are applied at 180 degrees to each other. As long as the thread tension is the same, the blank stays centered in the tube. The same applies to the counter-clockwise wraps coming from the other disc.
Note that thread tension can be set considerably less when using four strings.
The 4-string advantage is that the blank tends to stay centered in the tube without manual intervention. However, the side to side movement experienced with the 2-string version is not considered a detriment since you will want to guide the blank with your fingers anyway to assure all six strips are correctly aligned.
The 4-String version is offered for those customers having good results with 4-string binding, but wanting the advantages of a compact design, a mechanism protected from glue contamination and the ability to guide the blank right at the point of thread application.