The base plate has on both sides about 2 cm high adjustable jaws, with stick-on Moosgummipads that works like a vise. Here is when fixing the speaker a sense of helpers while holding the speaker during tightening up everything has a stable connection. It is important to ensure that the speaker sides are absolutely parallel, the jaws do not swivel. Small black screws may laterally be additionally screwed into the boxes housing, but this appears in little boxes not needed in heavy large boxes I do not trust this because of the size not to.
A few comments on the technical specifications of the manual differ from the data listed on Amazon.
The minimum radius (front edge holding jaws) is 273mm, the wall plate is inclusive cover only 260mm high.
Attention, for tilting is the total value of the top and bottom. In both directions only about 7 ° are possible (on Amazon indicated by 18 °). For strong tilting the holder is therefore not suitable. The maximum possible load is given very optimistic with 25kg, this is perhaps possible without tilt adjustment and absolutely horizontal alignment but about 10kg I would not go in person. My small 4kg Satellite hold but optimally also at full tilt and without additional locking screws.
Conclusion: The product is exactly what I was looking for - a stable visually appealing attachment to deface holding without the boxes additionally with screws.