Bear OPSB-400-AICF-B Bear Song IV Butterfly Knife Carbon Fiber Black Plain Edge. This Bear Song IV butterfly knife is the newest collaboration between BladeRunnerS (BRS) and Bear OPS. It is a lightweight flipper that is designed to be your go-to everyday carry knife. This B-400 model features carbon fiber laminate anodized aluminum handles with, stainless steel spacers and a swappable latch. The pivots have 304 bearing surfaces and phosphorus bronze washers. The black finished stainless steel clip point blade has a double tang pin design for great performance.