 The 55 mm diameter of the Nikon Z-mount is the largest in current use.It is much larger than the F-mount, the 46.1 mm Sony E that is used by all Sony mirrorless cameras, including those with a full-frame sensor but only slightly larger than the 54 mm of both the Canon EF and Canon RF mounts.It is also slightly larger than the new 51.6 mm diameter full-frame mirrorless L-mount from Leica, Panasonic and Sigma.