I also have a Kenwood model KH which takes the same mincer as the 900 series and searching around in my kenwood stuff I found the following screens that fit this mincer.
As far as I can measure with drill mandrils the largest screen has eight holes and the size of these holes is 10mm the second one is a 12 hole and the size is 8mm the third has 52 holes and the size is 3.5mm.
With a bit of further searching I founs a couple of older kenwood mincers and there was a screen there with just six holes and the centre worm one, so it measuresa aout at 12.5mm......The size of these screens is 28mm throat.
Do these sizes ring a bell with any other mixer screens please.