The Wolftoter (a/k/a Wolfton) spans the underside of the strings below the bridge, stretching to hook onto the A and C strings.  Select the specific ranges for your wolf note:  Low D-E (yellow tab), Medium Eb-F (green tab), and High E-F# (blue tab).   It is a little tricky to install as you will see after attaching one end to the A string, it doesn’t want to easily span the distance to the C string.  Looping dental floss through that second hook will give you something easier to pull on!   It has become less popular since there are so many options available now, and we have been special ordering as needed.