Text and picture copied from "Japanese Infantry Weapons" cincpac cincpoa Bulletin 55-45, 15 March 1945 :
"The Japanese Experimental Hand Thrown Mine is spherical in shape, 4.7 inches in diameter and weighs 3½ ounds. It is encased in a black, aluminium cover.
Attached to the main body of the mine are a carrying handle and fuse. The fuse is universal, instantaneous type, consisting of a striker, hammer, detonator chamber spring, detonator, and safety pin. It is filled with 3 pounds of a mixture of TNT, cyclonite and tetryl.
This mine is reportedly capable of penetrating 20mm (3/4 inches) of bullet proof steel and severely damaging lightly armored vehicles".