TRE Safety Thimble II - Black The Safety Thimble II is precision CNC machined 6061 aircraft grade aluminum. Designed for 5/16 to 7/16 synthetic winch ropes. Made in the USA! The Safety Thimble is 100% designed, manufactured, packaged and shipped in the USA. The design of the eye has a deep groove that provides protection against abrasion of synthetic winch rope. Designed to be used with a TRE Soft-Shackle or 3/4 (7/8pin) bow shackle, either by the pin or the body of the shackle.