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Discussion Starter · #1 ·
Normally, with carriage bolts I use only ONE washer behind the nut because of the square area just under the head of the bolt requires you to use a washer much larger than the bolt diameter.

Now I'm wondering which is correct. Do I need to put a washer under the head of the carriage bolt as well. I will be using 8 inch long X 1/2" inch bolts through 6"x6" posts. Thanks for the information.
 

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This is why I don't use carriage bolts on decks, you get much more bearing surface with regular hex bolts and washers on both sides. With carriage bolts I find the head is too small to prevent the head from cutting into the wood, esp fresh damp PT.
 

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Discussion Starter · #4 ·
Carriage bolts are designed to pull the square head into the wood . You only use a washer on the nut end
This is why I don't use carriage bolts on decks, you get much more bearing surface with regular hex bolts and washers on both sides. With carriage bolts I find the head is too small to prevent the head from cutting into the wood, esp fresh damp PT.
ChuckF- I'm using the carriage bolts on some very heavy framing of a Post & Beam barn. Carriage bolts are needed because the finish siding of the building will be over the bolt heads so I need a relatively flat head surface. I can't get a flat surface with a hex bolt. But I do agree with you that hex bolts with a washer under the head will prevent the bolt from sinking.
 

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You can get a flat surface with hex bolts by countersinking the bolt head flush with the face of the post. Looks good, and it is much easier to tighten or remove a hex bolt than a carriage bolt after a few years, since you can get a wrench on both sides of the hex bolt. When I countersink, I use a forstner bit to make the countersink holes, large enough to fit a wrench or socket in place.
 
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