To confirm which adapter ring you need, use the LEE System matching tool, HERE.
For the Canon EF 14mm f2.8L II USM.
For the Nikon 14mm f2.8 D AF ED.
For the Nikon 14-24mm f/2.8G ED AF-S NIKKOR.
For the Sigma 14mm F1.8 DG HSM - any mount.
For the Samyang 14mm f/2.8 ED AS IF UMC.