Wrench for Reverse Osmosis Canister – Wrench to tighten and loosen reverse osmosis canisters. RO Canisters can become very tight over time and changing filters can be a real challenge if you do not have the correct filter wrench. These are very handy to have around and are made of strong plastic to last just as long as your Reverse Osmosis system. Wrench for 2.5″ Canisters (most common) – This is the same wrench that is supplied with all BRS RO/DI systems and is by far the most common size for residential reverse osmosis systems and works with almost all canisters that use 2.5″ filters. Wrench for 10″ x 4.25″ and 20″ x 4.25″ (Big Blue) Canisters – If you have a jumbo reactor or almost any ‘Big Blue’ canister, this is the wrench you want. It is compatible with most canisters that use 4.25″ x 10″ or 4.25″ x 20″ filters.