Before buying a Jaws tool, make sure it fits your machine. It's a 4.5 mm tool for the standard machines with a ribber, and fits Toyota, Brother, Studio, Silver-Reed, Singer, Knitking, Juki - in other words, it fits the standard Japanese machines. You can always put a ruler in front of your needles and measure the distance from the center of one needle to the center of another.
Jaws will not fit Passap, which has a different needle spacing.
The little book that comes with Jaws is written for the Studio/Silver Reed machines, so the machine settings will seem quite foreign if you have a different machine. Still, once you get used to it, this is a very useful gizmo. The tools are not too to find if you contact the dealers on the internet, especial the Studio/Silver Reed dealers, either by phone or email.