Isoblue

The third hole with the steel insert is for screwing in the optional extension sections which can be used in between the shelf and the wedge-shaped leg. These give you either 35mm or 65mm extra height between shelves. If you're not using the extensions, ignore the extra hole and just assemble the shelf with the 2 dowels.

The bottom shelf has shorter legs with spikes fixed in them. 

Also the base shelf is thicker [30mm] than the standard shelf [20mm] according to Isoblue specs.

Actually just measured mine and the standard shelves are 19mm and the base is 25mm.

They used to be thicker in the initial iterations - more recently the base has been made in the same thickness as the other shelves (I have two 4-shelf Isoblue racks of different vintages, and only one has the thicker base - I asked about this when I got the second one).

thanks guys, Get now the third hole reason.

Yes it's vintage, notwithstanding I've 2 thicker bases it seems.

Other than that what -i can say is there's a 'listening' before and another one after.

Absolutely gorgeous now.

Hope to sort the damages ,though.

Antonio1,

It's critical to get Isoblue dead level from the base on up. Check each level as you build it. When I first assembled my Isoblue I leveled the base and then routinely stacked the shelves to find I had a wobble present - a gentle push on the top tier resulted in an audible clicking noise from several legs. Second time around I took great care to mix and match the legs and shelves to get a seamless and level fit. I also replaced all wooden dowels with new ones gently tapping the shelves into the legs with a rubber mallet to ensure proper seating. Run a cloth along all mating surfaces before assembly to be certain no debris is present. A few hours spend on anality during assembly will give great sonic results. From there you can upgrade with glass shelves and nuts & balls. Good luck and enjoy!