PARK TOOLS FR-5 SHIMANO-SRAM CASSETTE LOCKRING REMOVER BICYCLE TOOL
Works perfectly for Shimano Hyperglide lockrings
If you are trying to remove a Shimano Hyperglide lockring, then this is the exact tool you need. I took the lockring off in 10 seconds using this tool. Most important thing is to be sure you have a Shimano Hyperglide wheel as it only fits on this specific type.