Anycubic Vyper has a very tiny filament holder center, and only has a little bit of lip to stop the filament to fallout when rolling during printing. It becomes a problem for me during overnight printing where sometimes I am not close to the printer to look after the filament. The spool fall of the holder and prevents the filament to be smoothly pulled in or created a mess when the filaments gets unrolled.

This stopper will help to avoid the filament to fall of the holder. Just insert it to middle hole of the holder until end and it will stick there. Easy to remove as well. I used tree support when printing as it is easy to remove and use less filament.

ps. Thingiverse don't have Vyper as printer option, so I selected the Photon but it doesn't matter.

EDIT 1: Updated, adding .1 mm (from 26.2 to 26.3) to the inner circle diameter for better snug in to the spool holder hole.

EDIT 2: an improved, lock and forget version that replace entirely the tiny holder can be found here https://www.thingiverse.com/thing:4913369