A customer in Portland swore by using a 10mm wrench for everything, and it nearly cost me a derailleur hanger

He was adamant that a 10mm was the only tool you needed for most bike bolts, but when I tried to tighten his M5 derailleur hanger bolt with it, it rounded the soft aluminum head completely. I had to drill it out and replace the whole hanger. Has anyone else run into this 'one size fits all' advice causing real damage?

3 comments

3 Comments

fiona_young1mo agoMost Upvoted

Start by saying @nancybailey is spot on about the 10mm being too big for an M5 bolt. Those are usually 8mm wrench heads from what I've seen, but your mileage may vary depending on the brand. I've actually had the opposite problem where someone used an 8mm on a 10mm bolt and stripped it out thinking it was loose. It's easy to get tunnel vision with these tools, so checking the actual bolt head size before you crank on it can save a lot of headaches.

nancybailey1mo ago

What size was the bolt head actually supposed to be? A 10mm wrench on an M5 bolt sounds way too big. Most of those are 8mm or smaller. Did the customer just force it on there and call it good?

-1

avery_lopez1mo ago

Yeah that's a solid point from @nancybailey. I've definitely used the wrong size wrench before and just leaned on it until it kinda fit, not my proudest moment.