Shackles are U-shaped pieces of metal secured with a pin or bolt across the opening, or hinged metal loops that are secured with a quick-release locking mechanism.
Types of Schackles
There are three basic types of shackles. All meet or exceed U.S. Federal Specification RRC-271D, "Chains and Attachments: Welded and Weldless", and are made of alloy steel or carbon steel. They are available in painted, galvanized or self-colored finishes and use quenched or tempered pins. Class 1 shackles pass a rounded pin through holes at the base of the shackle. A spring-actuated cotter pin or hair pin holds the butt end of the shackle in place. Class 2 shackles use screw-pins that pass through an opening on one only side of the shackle. The pins use a key-like design and exhibit extreme deformation before failure. Class 3 shackles have safety anchors or chains that are held in place with a nut and bolt on opposite ends of the pin.
Specifications and Features
Shackles that meet Amendment 1 to Federal Specification RRC-271D are also available. Selecting shackles requires an analysis of specifications and features. Dimensional specifications include: pin or bolt diameter, hole diameter, width at eyes, width at bow, width between eyes, inside length, inside width at bow, outside diameter (OD) of eye, approximate weight, and estimated weight per hundred. Some shackles use English measurements such as inches (in) or fraction of inches. Others are measured in metric units such as centimeters (cm) or millimeters (mm). Performance specifications for shackles include working load limit (WLL), an amount that is usually measured in tons. Specialized shackles may carry additional specifications or provide optional features. For example, stainless steel screw-pin anchor shackles provide improved corrosion and chemical resistance. Trawling shackles have heat-treated bodies and square headed pins that facilitate tightening and loosening. Web sling shackles may be hot-dip galvanized or zinc-plated, and provide an ultimate strength equal to four times the working load limit. Shackles are used in a variety of lifting, pulling, and tie down applications. They are subjected to magnetic particle, proof load and fatigue tests and comply with U.S. military specifications (MIL-SPEC) such as MIL-C-46168D, MIL-C-53039A, MIL-P-53039A, MIL-P53022B, MIL-P53030A, and MIL-P-53084. Additional certifications include DWG 19207 12301040 and DWG 19207 12369003.