During assembly of the Tripp Trapp®, you will likely notice that it is not possible to fully tighten the upper bar of the chair, whereas the bottom bar can be tightened all the way. However, both metal bars are the same length, so how is this possible?
The seat plate and foot plate are the two widest parts of the chair and it is not a coincidence - these are also both the only parts that are not tightened by screws, but rather by the legs themselves into the pre-determined grooves which allow users to adjust for height and depth.
These plates are held firmly in place by tightening all the other components of the chair, especially the metal bars. The upper metal bar is extremely close to the foot plate during first assembly and its proximity to the foot plate (a wider component) will not allow for the upper metal bar to be tightened as far as the bottom metal bar, which is typically positioned far away from either plate.
When the child grows and the foot plate gets positioned lower, towards the lower metal bar, a gap will also appear there, as the gap is directly tied to the proximity of the plates. It is important to understand that the gap is not a safety issue, but a normal phenomenon and also the reason why wood is the material being used for the chair, as it allows for light warping of the parts under sufficient pressure, which holds everything firmly together.