A weight plate is a flat, heavy object, usually made of cast iron, that is used in combination with barbells or dumbbells to produce a bar with a desired total weight for the purpose of physical exercise.
Two general categories exist: "standard" plates, which have a center hole of approximately one inch (25 mm), and "Olympic" plates, meant to fit on the two-inch (50 mm) sleeves of Olympic barbells. Standard plates are usually paired with adjustable dumbbells and Olympic plates with full-size barbells, although standard barbells and Olympic dumbbells exist.
Weight plates may incorporate holes for ease of carrying (called "grip plates") or be solid discs (especially those used for competition). Non-competition plates often have variable diameters and widths, such as on the adjustable dumbbells pictured right, with heavier plates generally being larger in diameter, thickness, or both. Weight plates are typically round, although 12-sided and other polygonal varieties exist. Most plates are coated with enamel paint or hammertone to resist corrosion; more expensive varieties may be coated with chrome, rubber, or plastic.
Plates are available in a range of weights. Standard (1-inch center hole) plates are commonly available in 2.5, 5, 10, and 25 lb denominations, with 1.25, 7.5, 12.5, 50, and 100 pound plates less commonly seen. Commonly available plates with kilogram denominations are 1.25, 2.5, 5, 10, 15, and 20 kilograms, with 0.5, 7.5, and 25 kilogram plates less commonly seen.
Common Olympic (2-inch center hole) plate denominations are 2.5, 5, 10, 25, 35, and 45 lbs, with 1.25 and 100 pound discs less commonly seen. Kilogram-denominated plates are available in 1.25, 2.5, 5, 10, 15, 20, and 25 kg sizes, with 0.25, 0.5, and 50 kilogram discs less commonly seen.
Bumper plates are commonly available in 10, 15, 25, 35, 45, and 55 lb denominations, or 5, 10, 15, 20, and 25 in kilogram-denominated sets.
A few companies sell "fractional" weight plates weighing 1 lb (0.5 kg) or less. These allow "microloading" of bars to achieve very small increments in strength for advanced strength trainees. An alternative for microloading is to use a set of washers with one- or two-inch center holes.
Low-cost plates can vary widely from their marked weight. A 2% or 3% variation is not uncommon, with plates from some manufacturers frequently being 10% or more over or under (a 45-lb plate can weigh as little as 40 lbs, or as much as 50). Tom Lincir, founder of the Ivanko Barbell Company, has encountered 45-lb plates weighing as little as 38 pounds, or as much as 59 pounds.
Plates can be weighed, and the equipment marked (using a paint pen or other permanent marker) with the true weight.
Calibrated plates are available from high-end manufacturers; many advertise these plates as being accurate to within 10 grams (0.02 lb) of marked weight, which is the tolerance mandated by the International Weightlifting Federation for plates used in competition.
Standard (1-inch hole) "vinyl" plates are often sold paired with dumbbells or barbells as a low-cost option for casual strength training. These plates are made of cement or sand coated with a polyvinyl chloride sheath. The cement tends to break down over time and leak out of holes in the sheath, and the weights are less dense than iron so that fewer fit on a given bar.
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