I invented this some years ago, but never had it patented due to it would cost over $10,000 and they are very easy to make.
You can make these out of drinking straws or plastic tubing to fit over your crochet hooks. These will help you make more uniform bullion stitches,commonly called roll stitches. Cut a slit down through the straw/tubing as straight as you can, then trim one end off at a slant and rounded as shown here in this picture.
When you make the bullion st and after you make the last step of it, you just pull the Hook Sleevz off of your hook.