Eye bolts (eyebolts) are threaded bolts with a loop or eye at one end. The eye is used to anchor a cable, rope or chain. Eye bolts are rated for different types of applications and may pivot or swivel. Load-rated eyebolts are designed for vertical lifting, but are not recommended for angular lifting. Eye bolts that are not load-rated are designed for use with tie downs and guiding wires; however, they are not suitable for lifting applications. Specifications for eyebolts include maximum load capacity, threaded length, shank length, eye inside diameter (ID), eye section diameter or eye thickness, and total weight. Maximum load capacity is the maximum load which an eyebolt can handle. For fully-threaded eyebolts, shank diameter equals the thread length.
Thread sizes for eyebolts are measured in English units such as inches (in) or metric units such as millimeters (mm). Measurements for inch-based eyebolts include: 1/4, 5/16, 3/8, 7/17, 1/2, 5/8, 3/4, 7/8, 1, 1 1/8, 1 1/4, 1 3/8, 1 1/2, 1 3/4, 2, 2 1/4, 2 1/2, and 2 3/4 inches. Fasteners designated as #16, #18, #20, #24 eyebolts are also available. Designations for metric eyebolts include: M6, M8, M10, M12, M14, M16, M18, M20, M22, M24, M25, M26, M27, M28, M30, M32, M33, M35, M36, M38, M40, M42, M48, M56, and M54. As a rule, the numbers which follow the letter “M” indicate the number of millimeters in diameter. For example, an M6 eyebolt is 6 mm in diameter.
Eyebolts differ in terms of material and finish. Metallic eyebolts can be made of aluminum, brass, bronze, steel, hardened steel, stainless steel, titanium, or proprietary alloys. Aluminum is lighter than steel, but not as strong. Brass and silicon bronze are common copper-base alloys. Many different grades of carbon steel and alloy steel are used as fastener materials. Stainless steel may not require anti-corrosion coatings, but cannot be hardened to the same degree as carbon steels. Titanium, a metal that is used widely in the aerospace industry, is suitable for specialized applications. In terms of finish, eyebolts are often anodized, galvanized, or plated with gold, silver, tin, or zinc. Black oxide is an eyebolt coating that causes virtually no dimensional change. Phosphate coatings provide corrosion resistance and a better surface for the adhesion of primers and paints. Eye bolts with zinc chromate finishes are also available. Plastic eyebolts and rubber eyebolts may be suitable for some applications.
There are four specialized types of eyebolts. Forged eyebolts are forged instead of formed. These one-piece fasteners that offer higher load ratings. Screw eyes are screws with a head shaped into a loop or eye. They are often used in lifting and rigging applications, or to guide wire or cable. Shoulder eyebolts have a shoulder under the eye. Typically, the shoulder is installed flush with the mounting surface. Thimble eyebolts are designed with an opening that acts as a thimble for wire or rope to minimize wear. Pivoting eyebolts are designed to pivot 180°. The base of a swiveling eyebolt is designed to swivel 360°.