A thimble mechanism for retention of a shackle in a wire rope loop termination. In one preferred embodiment, a thimble device is provided for a shackle having a pair of opposed legs with each leg having an end with a width smaller than a depth. The thimble device includes a thimble body having an external arcuate edge with a rope groove for receipt of a wire rope therein. A central opening extends through the thimble body with the central opening larger than the width but smaller than the depth of the shackle ends. A keyway is provided in the thimble body extending from the central opening to the arcuate edge of the thimble body.