A black mesh basket for holes with 32 mm. Fits in e.g. Harvy, however, this basket is slightly narrower than the original basket (about 1 mm).
"Plant directly in the sponge or pre-germinate in the nursery or on damp paper towels and transfer to this basket once the plant has developed nice roots. This way, you save space in your large growing boxes."
The basket is blackand is 35mm deep
Drill with a 33 mm drill, e.g. this one