Currently there are 2 variants of the 1U Tile. For simplification we are calling these 1UF and 1UE.
1UF Tiles - FracRack Format
This is the original format and uses the FracRack approach to the rack section. The rack is constructed using lipless rails that allow the tile panel to extend the full 1U height. It also relies on the use of thin rails to maximise the available space for components and, if needed, a PCB.
The 1UF format offers the largest space between the rails.
1UE Tiles - EuroSynth Format
This is the newer variant and is technically the correct format as it uses lipped rails and so can work with existing EuroSynth rack parts.
The available space between the rails is smaller than with 1UF Tiles and will not accept 1UF pcbs that use the full height available in a 1UF rack
Both variants occupy 1U of rack space as can be seen in the drawing below which shows the fundamental dimensions for the 2 variants.
Not a tile format but refers to the finished rack assembly. Uses standard EuroSynth lipped rails with 1UF Tiles so the overall height is greater than the conventional 1U standard.