Designed to make adjusting the print plate a bit more comfortable on the fingers.
The nuts are intended to be a tight fit and you'll need to press down with a solid object (or failing that, a vice) to seat them. The nut is proud of the plastic by 0.5mm when fully in. Use the existing steel washer and a drop of oil when reassembling.
(Printed using my 'rough and ready' profile, so a bit blobby.)