As I soon need to add more weight to the shelf on which I store my 3D-printer, I decided to make some reinforcements to hopefully keep the shelf from collapsing.
This design utilizes three holes instead of just 1 with the original small pegs.

The pegs themselves are around 4,8 mm in diameter, and roughly 32mm apart (from center to center).

I can't provide you with any numbers of how much weight these will officially support, and it is of course on your own risk, if you decide to go above the recommended weight limit from IKEA.
I will, however, update this description with how much weight mine are supporting, once I've had them in use for a week or two :-)