Incandescent light bulbs are made in a great variety of shapes and sizes. The most basic shape has been designated with the letter A and is the familiar pear shape one might buy for home use. However, there are many commercial and industrial uses for A bulbs because of their universal practicality. The number following the A, such as 15, 19, 21, or 23 refers to the size. Specialty A bulbs include the A21 which is a large bulb, just over five inches in length. The A15 bulb is smaller, most commonly known as an appliance bulb. These bulbs may be clear for maximum illumination or frosted for a softer light. Some have a silvered bowl to reduce glare. Bulbs for rough service have extra filament supports and are excellent for drop cords or for places subject to vibrations. Linear incandescent bulbs look similar to long fluorescent bulbs, but they plug into a special fixture with two side prongs and range in length from about two feet to a meter. These lights enhance skin tones and are most often used in bathroom and have a long filament, which is fragile. Tubular bulbs have a standard screw base at one end and they are often used in signs, display cases, chandeliers and for track lighting.