Yes, no other accessories needed. The filter can be directly screwed on your camera lens. 

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EOS-FX,You can use Canon EOS EF / EFS Lens on a Fujifilm FX Mount Camera body,, Your canon ef 75-300 1:4-5.6 is canon EF mount lens and fuji x-a3 is X mount camera body. so the adapter ring fit for your camera and lens. but pls notice, your lens is telephoto lens,we do suggest you could use one telephoto lens bracket that could be attached to the tripod to increase its stability. because the canon lens could not adjust aperture,so suing our adapter ring could not adjust aperture 

there are 7 filter ring adapters, included 52mm/ 58mm/ 62mm/67mm/ 72mm/ 77mm/ 82mm, allows you use the nd filter on your kinds of size camera lens. 

Canon has at least 7 different 50mm lenses. You need to look on your lens to see what filter size it takes. It'll be written on the lens at the front, beside this symbol: Ø.