Let me tell you, there is no greater frustration than having a t-nut pop out, especially if you don't have access to the back of your wall.  None.  Not even when your car stalls on an arterial route during rush hour.  These little babies are here to save the day.  Simply place behind a notch on the t-nut, screw them in, and BAM! You've saved yourself from curling up in a corner, sobbing and repeating "I should have bought wafer screws" over and over. (These are based on actual facts....not, uh....my own experiences......)

Wafer Screws