If you installed some objective on your M25 head using one of our adapters that have 7mm height, you may encounter one issue. If all your objectives were parfocal (45mm, for example), and you add 7mm with adapter, you'll get one or more objectives on the head with 52mm parfocal height, and switching between objectives will require 7mm up/down correction of the head. Quite inconvenient.
To solve this problem, you can just add these 7mm extenders and match parfocal height of all objectives on the head. Just micro-adjustment will be required after switching an objective now.
Another application of these extenders is changing of working area of microscope mechanism. After long usage around same height, mechanism gets wear. If you add 7mm to each head port, you'll be able to move to almost new parts of gears.