Canon will be announcing the RF 50mm f/1.8 STM very soon. This lens comes with a small 43mm filter thread, a size a lot of you may not have in your kit. So here are a few options for the folks that like to use protective filters on their lenses.
Canon 43mm Protect Filter $31.95
B + W 43mm MC (Multi Resistiant Coating) Clear Glass Protection Filter $29.00
Marumi DHG 43mm Lens Protect Filter $24.99
Hoya Evo 43mm Antistatic Protector Filter $41.90
NiSi 43mm Pro Protection Filter $28.50
The Canon RF 50mm f/1.8 STM Specifications can be seen here.