If the snaps do not close with a loud click or at all, then most likely it is because the center prong was not smushed flat enough and is getting in the way. This happens when not enough pressure is applied when the snap is attached to the fabric or when the fabric is too thin (or both).
For more information, visit the Tutorials link on the top menu bar of KAMsnaps.com.
- Snap Pliers: http://www.kamsnaps.com/Instructions-for-Snap-Pliers-15.html
- Snap Press: http://www.kamsnaps.com/Instructions-for-Snap-Press-26.html