feather key

noun Machinery.
  1. a rectangular key connecting the keyways of a shaft and a hub of a gear, pulley, etc., fastened in one keyway and free to slide in the other so that the hub can drive or be driven by the shaft at various positions along it.
Also called feather, spline.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018