Two chain questions

1) What is the difference between the SRAM PC68 chain and the SRAM PC850 chain?
2) Do you guys use a chain wear tool to check the wear or do you just use a ruler?
2) Do you guys use a chain wear tool to check the wear or do you just use a ruler?
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Parktools :?:SheldonBrown
I've bought a new bike....ouch - result
Can I buy a new bike?...No - no result
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