For chains up to 530 size (all Triumph models as well as 99% of all motorcycles).
One side of the tool is used to break open a link in the old chain to remove it from the bike, the other to rivet the free link of the new chain. Use with a 19 spanner.
Brand Kellermann, type KTW2.5, superb quality.
Instructions video here.
12 month warranty.