Using a hammer

with or without the tire mounted

Extra Large: 8 x 16 x 2 cm - fits iPhoneX

the Park AWS-10 Multi Allen Key Tool has all the sizes you'll most likely need

Unior 617170 Chain Wear Checker Exclusive Using a hammerThe Unior 617170 Chain Wear Checker is a super handy, easy to use tool that will let you know if its time to change your chain. If you replace your chain early enough you will prevent premature wear to your cassette and chain ring. Who's this item for: Perfect for the at home bike mechanic, or really anyone who rides that likes to know the condition of their gear. Chain compatibility: Compatible with all chains. How does it work: It's pretty simple to