The Bear extruder uses a PTFE tube length of 50mm. It is the same PTFE tube as MK2S, MK2.5 (non-S) and MK3 (non-S). The original Prusa MK2.5S or MK3S extruder is using a PTFE tube length of 44.2mm which will be too short for the Bear extruder.

If you have an undamaged 50 mm PTFE tube from a MK2S, MK2.5 (non-S) or MK3 (non-S) you can reuse it.

The printed parts for the extruder include a PTFE tube cutter tool that matches the specifications required for the Bear extruder. The part name is ptfe_cutter_50mm_60deg.stl

Follow this guide to prepare the PTFE tube Trim PTFE Tube.