The default print head on the Prusa Pro HT90 is a high-flow print head. This allows a high volumetric rate which will let you print faster. The print head also has a fan control that uses a servo motor.
You can identify that the high flow print head is installed when it shows a blue stripe.
The high flow print head comes with a Revo High flow nozzle. Note that this nozzle is not resistant to abrasive filaments, as it is made of brass.
If you wish to print with abrasive filaments, use the Revo ObXidian Nozzle.
The nozzle can be changed by screwing and unscrewing by hand, no tools should be used. For that, follow the instructions here: Nozzle replacement (HT90) [進行中の翻訳].
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