This is a Hillman Square Key - 1/4" x 1 1/4". Square Keys are small bars of any length with similar height and width. They are commonly used in general industrial machinery, inserted between a shaft and a hub to prevent relative rotation. 

Features

• Great for mechanical applications: commonly used in general industrial machinery
• Prevents relative rotation: designed to act as a sort of anti-turn mechanism when inserted between a shaft & hub
• Used with rotating shafts and to attach gears to machine parts
• Strong, sturdy, reliable: made of high-quality steel
• Corrosion-resistant finish: zinc plating offers moderate protection against rust & corrosion
• Dimensions: 1/4" W x 1-1/4" L