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My shop foreman said to never use a 5mm Allen on a Shimano crank bolt, and after stripping one yesterday, I owe him a beer.
He insisted on the 8mm socket for the self-extracting type, a detail I ignored until the bolt head was ruined on a customer's Ultegra crankset.
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lewis.mila1mo ago
Man, I've used a 5mm on the actual bolt plenty of times without stripping it. You just need to be careful and not crank it like a gorilla. gray875 is right about the preload, but that bolt can handle it if you're not heavy handed.
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gray8751mo ago
Yeah, that's a pricey lesson. The 5mm is just for preload on Hollowtech. The 8mm socket is for the actual crank bolt.
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the_piper1mo ago
The real problem is that worn 5mm hex keys flex too much. I learned that after rounding off a bolt on my own bike. Gray875 is right about the bolt's job, but a cheap tool makes it way easier to mess up even if you're being careful. You need a really good quality hex that fits tight in the bolt head.
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