Rohloff HG-IG-CheckCog wear indicator for HG and IG sprockets Rohloff developed the HG-IG-Check tool to be able to quickly determine the condition of Shimano HG or IG cassette sprockets. The tool will indicate when the cogs are on the verge of being too worn out, therefore preventing chain skipping. Cassette cogs should be checked before long trips or before replacing a chain to determine if the new chain will skip on the old cogs.Â