A kit that enables you to make any size or length cord/wire retractable.

[edit] alright... by supplying a number of different cylindrical spool heights, diameters with exchangeable, different strength springs (if that is how they work) specified for different types of wires, that you can look up in the manual that comes with the kit.
-- leinypoo13, Jan 22 2008

Forty or so years ago, before seatbelts were built-in, and automatically retracted, one could buy seat-belt retractors as an add-on. These were much as you describe, spring loaded spools.
-- csea, Jan 22 2008



random, halfbakery