Size: 5/16"Long Arm Length Range: 3.656" - 3.844"Short Arm Length Range: 1.156" - 1.344"Material: Hardened Alloy SteelA Hex Key Is A Six-Sided Shaped Bar Bent At A 90 Degree Angle At One EndDesigned To Be Inserted Into A Like-Sized, Hollow Recess Of A Socket Screw To Manually Tighten Or Loosen The FastenerEither Side On The Key Can Be Used For Convenience