Depends on your cranks and the ring you are using. 6mm ought to be sufficient for your purpose, even with a fairly thick chainring though.

With a very thin chainring and a spider with deep recesses, any longer than that means you may have to grind down the receivers (not a good time).

Place the ring you will be using on the spider, and place a chopstick or something through the bolt hole. Line up the end with the bottom of the bolt recess, and then mark the opposite side. This will give you the maximum receiver depth. Your chainring bolt needs to be around 1mm shorter than this measurement.

 

ah, measure it, rather than asking silly questions on the internet.

thanks!

 

ah, answer the question, Mr. Know-It-All, instead of being a jerk.

:thumbsup:

 

I have yet to see any chainring/spider combo that did not work with a "single" bolt set, even with the thin Surly steel rings.

If for some reason the recess in the chainring is too deep and the bolt bottoms out, just flip the ring and have the recess against the spider.