It is a cap to improve the sliding of the spring . It had been increasing the number . To respect the original , little tinkering .
Failed to read the original STL file , it was re- edited .
The X -axis 90 degrees and rotated .
To recommend that you print using the ABS filament . I think that PLA is dissolved. It is better to be output in a different 3D printer. Changing the filaments there is a risk .
(June 24, 2018) It seems to be popular, so I fixed it a bit.