The tool that the bases came with!  Or, any wide, flat, piece of steel.  The long middle part of a typical cheap "church key" can opener with both rounded (bottle) and pointy (can) ends would work OK.  The essential knowledge is that the nut will not be tightened beyond the point that a simple flat pry bar would run into the bolt and be bumped off.  Getting the nut off is harder(*), and would require using two smaller flat-head screwdrivers held in a "cross grip", like a plumber would do. (That's if you don't have the double-tipped tool.  The mistake people often make, is trying using the double-tipped tool to tighten the nut -- they bend the tool tips.  You tighten with the flat part of the tool, which gives you more torque and won't set the nut beyond the end of the bolt.)

[Edit: Such precision tightening requires the presence of the 2mm thick lock washer between the nut and the base plate.  Your photo shows one, but if future searchers are DIY with no tool, maybe washers were missing too?]

* "That's what she said." (Sorry, been watching to much of the BeoTalk / BOTF bros.)

I couldn't see if BeoWorld has the Floor Base 2119 manual online for Gold Members, so have uploaded it below.  It does not carry a copyright notice, and besides it's a protected use per 17 USC 107 anyway.

 

Thanks a lot for the manual. Any idea what that tool is called or where I get one? Thanks

Courtesy of the BeoTalk Discord:

"Needlenose pliers with pins in the ends are a commonly available tool good for this, although intended for installing or removing snap (retaining) rings. E.g. Channellock # 927. (You must also set its pins long-ish so the angle doesn't contact the interior of the bracket, but less problematic vs. plain needlenose. There's plenty of heft in the plier hinge to crank off most any such nut: it's a plumbing tool, not a tiny lightweight electronics tool circlip-grabber.)"

A later note pointed out that the nose pins which come with that tool include right-angle pins which may be used from the side, because the usual snap-ring tips won't reach over the 18's end bolt that long.  Also pointed out was that nut is completely hidden underneath a floor base, so one could just use ordinary pliers on it and nevermind the nicks and scratches.  (If you're using wall brackets I'm not sure if it's totally invisible when installed?)

Here are the pics with those messages:

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Alternate method: Since apparently you aren't the first person who has been screwed (ha-ha:-) by the heavy-handed assembly crew, ask your dealer to send out a technician to fix this "manufacturing defect" -- if the tool bends, it's their problem the nut was over-torqued, not yours.  After enough truck rolls, maybe someone will get the message if every BL18 consumer delivery has a service call for it!

Thanks for your help.

I brought my Beolabs to my B&O dealer today (he's not far away). The first thing he did was getting his own B&O tool and some sturdy pliers and bent the tips of his tool into position. He said it's usual that they keep bending, without acknowledging this fact. With one precise move, the first nut came off. He said that he has some experience doing this... The nut of the second speaker was way harder to loosen. In the end he wrapped a thick cloth around bolt and nut and unscrewed the nut by using a wrench. It didn't work instantly and required quite a bit of force.

Now both my Beolabs sit tightly in their baseplates and everything is fine.