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I'm trying to restore an old park bench, and I am struggling to unscrew the bolts. The heads have this wide (~12-14 mm) "flat cross" pattern that I have never seen before (see photo), and I don't have any screwdriver that nearly wide enough to get any kind of grip on them.

My googling attempts to find the right tool have been futile. It might be because I don't know exactly what to search for, but common screwdriver bit sets don't seem to have anything approaching that kind of size.

What would be the right tool to unscrew these and where could I find it?

bolt head

And, for what it's worth, square nuts at the back:

squarebut

Update:

Drilling successful! One down, 23 to go...

drilled bolt

Nicolas Payette
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6 Answers6

31

Looking at the condition of the nut and the minimal profile of the head, I'm afraid the better question may be "how do I get these out with minimal damage to the wood?"

I'd take a drill to the end with the nut. Hold the nut with pliers if the nut-and-screw assembly is prone to spinning. Choose a drill slightly larger than the screw itself. You can either drill all the way through the nut until the remnants of the screw and nut are completely separated, or drill most of the way through and then hammer a punch or nail set into the drilled hole until the screw/nut shears away.

Greg Hill
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19

I would use a small grinder ( Dremel) with a cut-off wheel and cut the nuts off.

blacksmith37
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Normal flathead screwdriver in theory

I believe these are simply used to make it easier to apply a flathead screwdriver with at most 90 degrees of turn adjustment needed. So in theory you can just put a flathead on it, a spanner on the square nut, and you're done.

In reality, better with a Dremel on the nut

Considering the level of rusting though, it's highly unlikely you're going to get anything to part company. Most likely the screwdriver slots are going to give way, or for a second possibility the head could shear off. I'm with @blacksmith37 here - the best solution is to simply cut the nut off, and then use something of the right diameter as a drift to knock the bolt out of the front.

Graham
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I would use a grinder attachment on an electric drill to carefully grind off the nut. Next I would use a “EZ out” to back the bolt out of the hole. The EZ out is available at most hardware stores for a few bucks.

Skywriter
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Depending on the aesthetic requirements, an angle grinder from the back may be the fastest option.

fraxinus
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I'd start by soaking the threads with penetrating oil of your preferred type. Then the next day fit a suitable 12 pointed socket over the nut and see if it spins off.

Option 2 is to get your assistant to hold the socket still while you use an impact screwdriver and hammer on the front.

Third, try adding some heat to the nut, ideally a small gas torch or perhaps a high-powered hot air gun. Avoid burning the wood though. Then repeat with the leverage and impact screwdriver.

Last resort is to drill either end. It could work out easier to drill the head because its already got a crosshair there, and you theoretically have less metal to drill through.

When you choose new bolts, consider stainless steel or at least galvinised steel, and pre-grease the threads, ideally with an antiseize compound.

Criggie
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