This is a 10w T4 tube that is 352mm long including the pins at each end. It is used in under cupboard lights and some illuminated mirrors.
Please be aware that there are multiple sizes of 10w T4 tube availableThis 10w bulb is 338mm long excluding pins and 352mm long including pins. When buying T4 lamps, it is important to purchase lamps from the same manufacturer as the light fitting that you have or at least check the size very carefully. T4 lamps vary between manufacturers in tube length and cap style, so are unlikely to fit other manufacturers fittings.