Check the listing for details. microSHIFT Acolyte RD-M5185M-B SpringLock Rear Derailleur - 8 Speed, Medium. Color: Black, Condition: New. Listed at 38.92 USD. The heart of this microSHIFT Acolyte derailleur is the innovative SpringLock system. By pairing a customized linear rate high tension spring and a dual stage activation mechanism, we’ve developed a system that can provide substantial chain security when you need it and can be turned off when you don’t. To engage the clutch, turn the engagement bolt clockwise until it clicks. There’s no way to overtighten the bolt. To disengage the clutch for wheel removal, flip the switch. It’s that simple.Upgraded cage design provides improved chain wrap and retention. Innovative SpringLock chain retention keeps chain in place over rough terrain. Direct path cable routing for smooth and responsive shifting. Compatible with 12-42t and 12-46t 8-speed cassettes. Compatible with Acolyte shifters only. Item.