Is this an unsuitable cassette lockring tool? I can't get my lockring tool to fit my cassette's lockring. The tool is about 1mm i diameter bigger than the lockring, although they have "hills and valleys" that line up.

Here's the lockring:



Here's the lockring tool:



Here's the tool in the lockring before I try to engage the lockring with the tool:



And here's the tool nestling on top of the lockring, but it doesn't fit in at all:



The lockring says "LB SHIMANO" on it. The tool says it's compatible with Shimano Hyperglide. Do I have the wrong tool for the job?
I think thats a Shimano freewheel, rather than a cassette. 

A Shimano freewheel needs a tool like a Park Tool FR-1 (or FR-1.2 or FR-1.3), which has 12 splines and a diameter of around 23 mm rather than the Shimano cassette tool (Park Tool FR-5 or its variants), which also has 12 splines but a diameter of around 23.4mm. 

See this link from Park Tool on how to remove it.