RE:RE:RE:RE:Looks like.....The biggest DTC (deBeers) sieve size is number #23, which has circular apertures of 10.31mm.
The critical size for stones not passing this sieve is given as 9.2 carats.
In practice, diamonds are not regularly shaped so how they present to the aperture could affect if they go through or not. eg long thin ones might go through end-on but not sideways.
It might be that 10.8ct was arbitrarily chosen as the cut-off as a result of statistical results on stones that don't pass sieve #23.
Maybe someone else knows?