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What-is-a-type-a-lamp-light-bulb, the most commonly used a-series light bulb type is an a19 bulb (or its metric/iec equivalent, the a60 bulb), which is 19⁄8 in (2 3⁄8 in; 60 mm) wide at its widest point and approximately 4 3⁄8 inches (110 mm) in length. other sizes with a data sheet in iec 60064 are a50, a55, a67, a68, a71, a75, and a80.