Blind hemming can sometimes be a little tricky so the blind hem foot (G) goes some way to help improve this technique.  The foot has a metal guide in the centre and three lines struck on the underside.  During blind hemming, the fold of the fabric fits snugly against the guide in the foot for accuracy whilst the lines underneath help to prevent unnecessary slipping.  The needle will swing over the metal guide creating slack in the upper tension so that the pick of the stitch is almost invisible.

A tricky technique made easier.