A useful wee attachment for those who are worried that they, or children they are sewing with, might inadvertently slide their fingers under the needle, it acts as a marker of the zone which should remain finger free.

These can be a teensy bit fiddly to attach, however this photo is a good guide to show how the end with the loop in it slides around the screw which holds your presser foot in place.  Simply loosen the screw enough to let the guide in, then tighten when its in place.  Remember that the U shaped piece is on the right to allow you to access the needle in order to thread it.