The Crank Brush is the first climbing brush that also tightens loose climbing bolts. It features a large, dense boar's hair brush for cleaning holds and a socket in the end of the handle so you can tighten loose bolts you come across at the crag. It's made of 50% glass-filled nylon which is the same material bicycle tire levers are made of, which makes it lightweight and incredibly durable.
The socket in the handle is a 9/16 SAE which fits 3/8" expansion bolts and 1/2" sleeve bolts. Which are the most commonly seen bolt types in North America.
The Crank Brush fits in most chalk bags. As a rule of thumb, check to make sure your chalk bag has an elastic loop for a brush, rather than a loop of static material. Most chalk bags do have an elastic loop, but some do not.
Check out the article by climbing magazine: https://www.climbing.com/gear/unique-find-a-brush-that-tightens-bolts/