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I have a sofabed whose back is fixed to the bed by bolt and nut. When I try to loosen the nut by wrench, the bolt and nut move together. There are no rust. How shall I loosen the nut?

Update: the head of bolt has a shallow hex hole. I have got help from another who used hex wrench to stick into the hole of the bolt head and fix/rotate the bolt, together with a regular wrench to rotate the nut.

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What does the head of the bolt look like? Is it accessible? –  James Van Huis Jun 21 '11 at 19:20
The head of bolt has a shallow hex hole. I just learned that a hex wrench can stick into the hole and rotate or fix the bolt. –  Tim Jun 21 '11 at 20:03
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4 Answers

up vote 5 down vote accepted

Best way: put a wrench on the nut and the proper driver or socket into or over the head of the bolt, and turn one while keeping the other stationary.

Second best way: put a wrench on the nut, and a pair of locking pliers on the shank of the bolt. You WILL damage the threads of the bolt; just try not to cause so much damage the nut won't come off. This is the only way besides cutting to remove a carriage bolt, which has a flat or a smooth dome head that can't be "locked on" with a socket or driver, or to otherwise remove a nut from a bolt when you can't get to the head.

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Thanks! There is a hex hole in the head of the bolt, and a tool called hex wrench can stick into it and fix/rotate it while loosen the nut by another wrench. –  Tim Jun 21 '11 at 20:14
Yep, also called an Allen head. You should be good to go as long as you have an Allen wrench of the right size. –  KeithS Jun 21 '11 at 20:16
So long as it's not a carriage bolt, I'd first try putting the locking pliers on the head of the bolt, before the shank. Sometimes with a carrage bolt, it won't slip until after a couple of turns, so you can smack the shank end with a hammer to expose the head, then clamp onto it with locking pliers. –  Joe Jun 22 '11 at 0:51
In the past I have used a very small drill bit thats made for removing stripped screws, into the actual bolt while holding the nut with a wrench, work perfect for situations where the head of the bolt isn't accessible, another option using a drill, or impact is to pull as hard as you can on the nut in the direction of removing it, in hopes that the head of the bolt will snag on the other endbe tight enough to allow the nut enough pressure to loosen –  user2140261 Feb 22 at 17:08
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You need to to get someone on the head of the bolt to stop it from spinning. The tool depends on what the bolt head looks like and how much space you have to work with.

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Penetrating oil.

Seriously though, you'll have to find the head of the bolt and hold that while you turn the nut (if you're not already doing that, which it sounds like you're not).

If you hold the bolt but are still unable to turn the nut, you may indeed need a little penetrating oil. Spray a liberal amount of the oil on the nut and bolt, wait 5-10 minutes (longer if the bolt is really rusty, which it doesn't sound like it is in your case) then try to loosen the nut again. You'll want to put a towel or rag under the bolt to catch any excess oil that may drip off.

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Assuming it is a carriage bolt with a smooth dome shaped head and without a square shank on the underside.

Method 1: Squeeze some superglue around the head of the bolt. Wait a while, then try unscrewing the nut again.

Method 2: Drill a small hole, say 1/8 inch diameter at the edge of the dome head, at an angle, say 45 deg.to the bolt shank, about 1/4 inch deep, insert the drill into the hole to lock the head from rotating when the nut is being unscrewed.

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