mount plates with centre hole diameters of 27 millimetre (1.06 in) through to 31 millimetre (1.14 in). This variation may prove very problematic if plates are mixed and matched. As plates with smaller holes may not fit the larger diameter "standard" bars. Gauging this by eye is very difficult, so taking the bar (or a micrometer gauge) to check that new plates will fit an existing bar is essential. Alternatively a larger hole plate may rattle or spin on the smaller diameter "standard" bars unless very securely collared. Small circular spring clamp collars are most often used to secure the weights though more permanent fixings are available. Other variations include spinlock end bars with screw on nut collars and many others. The thickness of the grip section is most commonly in the United States or in Europe, but can be thicker or thinner, depending on quality. Neither bar weight nor length is standardized like men's or women's Olympic bars, and can range from to . They are rarely rated for more than of loading. The bar itself can weigh anything from 4kg to 10kg The main advantages of "Standard" or "One Inch" barbells and weight plates are that they are often easier to store and take up less room; the bars may come apart into two or three sections, weigh less, may also be convertible to dumbbells, and are usually much less expensive than Olympic weights for those on a budget. Weight plates come in cast iron, or coated cast iron, tri grip, or far thicker and cheaper vinyl filled with concrete. Dumbbells Dumbbells are the equivalent of one-handed barbells, with a gripping surface approximately and a total length that rarely exceeds . Adjustable dumbbells are the most prominent use of "standard" weight plates (those having a to center hole). Some dumbbell sets come with an attaching bar to convert the pair to a single barbell. EZ curl bars Originally known as a Dymeck curling bar after its inventor Lewis G. Dymeck, the EZ ("easy") curl bar is a variant of the barbell that is often used for biceps curls, upright rows, and lying triceps extensions. The curved profile of the bar in the grip region allows the user's wrists and forearms to take a more neutral, less supinated position. This reduces the risk of repetitive stress injury in these exercises. However, when performing the biceps curl, using an EZ