Here is my collection of GARDENA (and non-GARDENA) holders.
The brackets are very stable due to the stiffners, but are still designed to save material!
The holes are designed for Countersunk SPAX Ø4mm. Ø3mm or Ø3.5 will also be sufficient. I recommend using A2 Stainless Steel screws.
The author marked this model as their own original creation.