Off-topic: USB gizmos

[Patricia M Godfrey pmgodfrey@xxxxxxxx]

My MFC (Brother 3100) came with two little thingies: a cable tie (classic
plastic strip with a hole at one end that one threads the other end
through to create a loop) and a "filter core"-- a heavy rubber or plastic
cylinder, about 1.5 in. long and .75 in in diameter, opening clamshell
fashion along its long axis. The directions say to loop the cable tie
around the USB cable, 2 inches or less from the printer end of the cable,
draw it tight, and then affix the filter core around the cable between
the tie and the printer connection. Now these things are certainly
necessary: if they come loose (as they recently did), the MFC goes
haywire, reinstalling its printer ports whenever one warm boots. But what
the heck are they and what, exactly, do they do? I HATE to just blindly
do things without a clue to what they are and how they work, but I've
never seen anything like these in my books or in magazine articles. Any
real techs here have any ideas? One assumes from the name that they have
somethihng to do with RMI filtering, but aren't USB cables supposed to be
insulated?
Patricia