3/16" heat treated steel crank gear woodruff key. This key is common on SBC, BBC, or Hemi engines to locate the crank gear on the crankshaft snout. Overall height is .300" and width is .188".
It is important to measure the key in the crank to see how far it sticks out then measure the depth in the gear before installing to make sure the key is set to the correct depth.
Different gear manufactures have different depths in the gear. Keys are sold individual