The "Moser Flex" tailpiece features four V-shaped string-hanging options, to allow for various "afterlength" distances for your four strings. It can provide yet another valuable, easy-to-use tool for individual sound tuning of a double bass. It allows you to make adjustments to account for peculiarities of your instrument, or tailor the tone and feel to your personal preferences.
So, as you can see from the photos, lots of variations in string lengths are possible - just a handful are shown, but the sky's the limit! Why does that even matter?
What we've learned is that the short answer is this: Having more control over the "afterlength" (the non-playable range of the string between the saddle of the tailpiece and the bridge) can actually have a notable impact on tonal quality; its own vibration, audible or not, can work for or against the overall sound of the string and the total instrument. (As an example, some luthiers tune the afterlengths to 2 octaves and a fourth above each string's pitch.) With a traditional "fixed fret" tailpiece, most luthiers can only "get close" across the 4 strings - with this tailpiece, you can adjust each string's afterlength individually. By locking the ball ends of your strings into one of the many choices, you can alter the length of each string's afterlength.
So it has potential benefits for the timbre of your instrument. But did you know that adjusting the afterlengths can often help to mitigate problem wolf-tones, too! So there's another common benefit, as well.
What's particularly attractive about it is that it has its useful adjustability - and yet still maintains a reasonably traditional look. We're told that the tailpiece is made of pearwood, but it has a hard opaque finish of satin (not shiny) laquer on it that gives it a traditional unfinished ebony look.
Note - some of the photos are of the older model; the current model (as shown in the first photo) also has two ADDITIONAL holes for extended length string mounting for one or two longer strings.
This tailpiece INCLUDES a Kevlar tailpiece cable and leather "tiles" for vibration damping.