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Brake Boss Dia

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Old 03-20-11, 02:53 PM
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ak08820
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Brake Boss Dia

I was trying to install a front rack that I bought from Nashbar. It is supposed to be anchored to the front brake bosses, but the holes in the tabs are smaller than the dia of the bosses. So, I will need to enlarge the hole and am wondering if 5/16 is the correct size for the drill bit, which I need to buy now as my drill bits stop at 1/4". I don't own a caliper. Got to be careful with Nashbar. I am stuck with some brake cables, too, which don't fit an MTB and nothing was mentioned in the description.
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Old 03-20-11, 03:02 PM
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The bosses are 8mm which is very close to 5/16". But before you drill make sure you want or need to. Usually these racks have a 6mm hole and bolt against the end of the boss so the canti or V-brakes can still be used behind the rack.

If you aren't using the boss for the brakes, you could drill the rack, but you'll also need a bushing or stack of spacers to fill the boss so the bolt can bear on the rack.

Yes, you do have to know what you're buying anytime you shop on-line. For instance there are two common heads used on brake cables, one for drop bar levers, and one for upright bars (there are exceptions). I'm sure if you recheck the description you'll see that you missed a detail.
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Old 03-20-11, 03:40 PM
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You are correct! Now, when I looked at the diagram more closely, I see that the brakes are behind the tabs not in front and it did come with a couple of plastic spacers. Thanks!
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Old 03-20-11, 03:52 PM
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FBinNY 
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Originally Posted by ak08820 View Post
You are correct! Now, when I looked at the diagram more closely, I see that the brakes are behind the tabs not in front and it did come with a couple of plastic spacers. Thanks!
Good thing you had to ask the size before drilling.
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Old 03-20-11, 06:56 PM
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Originally Posted by FBinNY View Post
Good thing you had to ask the size before drilling.
I don't understand it, I drilled it twice and it's STILL too big!
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Old 03-21-11, 02:48 AM
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Originally Posted by HillRider View Post
I don't understand it, I drilled it twice and it's STILL too big!
Have you tried running the drill in reverse?
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