Flower bulbs or tubers, regular in shape, can be sorted by circumference, expressed in sieve size, by means of a garden riddle (1). The sieve openings are a little larger than the actual circumference measurement, especially if the shape is slightly irregular, as with tulips.
The garden sieve consists of a number of separate wooden sieve plates (approx. 60 cm) in which there are holes of different diameters (approx. 2.5 cm; 3.5 cm; 4 cm; 4.5 cm). These rectangular or round plates fit in a wooden holder with which you can sort the bulbs or tubers in ascending size while shaking. [MOT]
(1) Bulbs and tubers that are irregular in shape (and also rhizomes) are also sorted by size, expressed in 1st, 2nd and 3rd size but this is mainly done by hand.