Butler Tray Hinges with rounded ends have traditionally have been used on tables or trays with folding leaves. These hinges hold leaf in upright 90 degree position and snap open to support leaf in flat 180 degree position.
Recently butler tray hinges have been used for keyboard trays on computer desks. Hinge allows drawer front to open flat for keyboard, when in use, and fold upright when not in use.
Butler-style coffee tables have four small half-round leaves, one on each side of table top. Each leaf requires two hinges/ one pair. A total of 4 pairs of hinges is necessary to redo an entire table. See picture below.