These are very strong pinching clips. Plastic and very tight. For a "nicer" pinch, get the "EASY PINCH" clips.
SEE how to use them! This is a video by the fabulous Sam Biddle from the UK - Clear Clips that will allow you to pinch your acrylic or gels. Apply the clip along the tip up to the sidewalls. When using with gels, cure gel 30 seconds in UV or 5-10 seconds in LED before applying clip. Since the clips are clear, the light will cure through them. Set comes with 5 clips and a clear plastic case to provide easy storage and travel - plus 1 bonus clip in case you break one!