In the product description specifying the exact extent is missing. That is why I share them with you here:
Depth of the L-support (leading edge to the wall): 24.5 cm
Thickness of the L-carrier: 2 cm
Depth with completely pushed in extension: 39 cm
If you want to see the assembly instructions in advance: You can find them at hama.de by entering the item number 00110931 in the search box.