 This is due to the stamping die behaving like a cookie cutter and causing a slight rounding of the upper edge of the cut clip.The snap ring must always be installed such that force is transmitted to the retaining groove from the rounded side of the ring, not the rough/square-edged side.If a snap ring is positioned such that its flat side is pressed into the rounded edge of the groove then when load or force is applied, the flat edge of the snap ring will "bite" into the rounded edge of the retaining groove.