Newtonian telescopes are sensitive to the fact that the main and secondary mirrors are exactly at the expected angle. Otherwise their performance deteriorates, making night work difficult or even impossible.
Fortunately, the secondary mirror can be finely adjusted to achieve this, but some kind of auxiliary tool (screwdriver, Allen key) is required. There is some danger in this operation: if it slips out of your hand and falls onto the main mirror of a Newtonian telescope, it can destroy it. Not to mention that these tools are not available when you need them most! By inserting collimation screws, both problems are solved in one fell swoop: the secondary mirror becomes manually adjustable.
The collimation screws recommended for Newtonian telescopes are compatible with most 13 cm or larger Celestron / Orion / SkyWatcher Newtonian telescopes (including Dobsonian designs). The shorter one is 35 mm long, the longer one 45 mm.