I use 4 steel wire clamps (6mm) per shelf (fastened on the vertical posts) to place the shelf at every height I wish. A lot of people do so.Keep in mind that the shelves are not adjustable and some larger helmets will not fit, like the Rubies Supreme Vader. But a good value for an outstanding shelf.
I do see how the clamps come in useful, however, it does ruin the clean look of the shelf a bit, IMO. This shelf would be perfect if it was a few more inches deeper and wider...along with adjustable shelf support.
Here is my mod to add an additional shelf to my Ikea Detolf.
8-32 threaded rod cut to 12.75"
Nylon L brackets
Glass or Plexiglas cut to 15" x 11.5"
I got everything at Lowes, but they are common parts to any hardware store.
Attach the threaded rod with the L brackets as shown. The little cylinders are to keep the glass off the threads, but are not essential.
So that's why they never have any in stock when I visitI have one or two Detolfs.....
I would highly recommend getting some helmet stands (chrome kitchen towel holders) for your lids.
Not sure if someone else did it as well, but here's the cabinet I did with two detolfs, some MDF, a bit of trim, and some extra hardware I had lying around.There was a guy on here that joined 2 together, it looked pretty sweet.