As makers of the Sundance pollen traps, we know something about the
subject.  Peter Chaing Mai said "I have been measuring the holes on a
pollen trap.  The bees pass through the holes to remove the pollen.  They
are drilled through plastic and are 3/16" (4.76mm).  I am proposing to use
a metal mesh and that is available only in metric measure so the closest
diameter holes will be 5mm.
Does anyone see any problem with the increased diameter, it is small (5%)
but are bees going to retain materially more pollen?"

For some reason, the manufacturers of wire screening use English (or,
Imperial) measures rather than metric.  The mesh counts refer to how many
openings are in an inch of fabric (screen).  Well-designed pollen traps use
five, seven and eight mesh for the trap itself and 16-24 mesh for the
screen in the bottom of the pollen trap.  HOWEVER, the number of openings
to the inch is not the only important factor and the wire diameter needs to
also be taken into account.  Wire diameters are also expressed in English
measurements.  Combined, they produce the amount of open area in the mesh
which is very important when considering damage to bees, amount of pollen
retained for brood, and trap ventilation to retard mold damage to the
pollen.

The OAG trap is the ancestor of all modern pollen traps, but has major
design deficiencies.  Most modern pollen traps are constructed with
screen.  Some use perforated metal, but these have a nasty habit of
removing bee wings until the burrs are removed by several days or weeks of
wear.  I have never seen a plastic performation that was not junk.
(Sorry.)  Perhaps such a trap exists and I have not seen it.

Those who want to make an improved trap need to make a list of important
attributes, such as:

1.  Collection of 50%-60% of pollen, with the remaining amount going to the
brood nest.
2.  Bee escapes that do not slow outgoing traffic from the hives.
3.  Drone escapes that will largely not be used by incoming bees to avoid
the trap.
4.  Means of reducing mold by distributing pollen more or less evenly into
a collection drawer.
5.  Means of preventing rainwater from entering the pollen collection area.
Etc.

Hope this is helpful.

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