I needed this for my Loose Filament Holder, as the filament would jump off the UM2 supplied filament guide, I needed it to be captive, and found NeonGreen's design (https://www.youmagine.com/designs/improved-filament-guide-for-ultimaker-2) which was almost OK, but does not captively hold the filament in the orientation required, so I took that as inspiration and modelled one that will hold the filament captively on both sides.