Snap spring. Models: BG 66 C-E D BG 66 C-E Z BG 86 BG 86 C-E BG 86 C-E D BG 86 C-E Z BG 86-D BG 86-Z SH 86 SH 86 C-E SH 86 C-E D SH 86 C-E Z SH 86-D