large half-dome-shaped nail
A nail with a large, rounded head resembling a crab's eye, used in construction and woodworking for decorative or functional purposes.
Crab-eye nails are used in this fitting.
Compound of 蟹 (かに, 'crab') + 目 (め, 'eye') + 釘 (くぎ, 'nail'), referring to the nail's head shape resembling a crab's eye.