A query came up on another URB board I moderate:
http://pub41.ezboard.com/fthedudepitfrm37
"I asked this over at Thomasik but they're puzzled too!
Can you help?......OK, this may qualify as a silly question but....
I use Weichs and every set I bought has a small piece of tubing slipped over the D string.
I've asked just about everyone (including the UK distributor) what the purpose of this mystery component is but no-one seems to know.
I've tried using it at the string/bridge contact point which seems the only logical application but all it did was to cut the sustain.
There has to be a reason for it to be supplied...but what?
Your answer eagerly awaited!! "
I remember using the tubing on violin E and A strings sometimes, which cut down on the harshness a bit, but a bass D?? Anyone??