Selling a new, never installed or used, Robertson electromagnetic fluorescent light ballast number SP48. Made in the USA by the Robertson Transformer Company of Blue Island Illinois. It is used with any of the following single bulbs – F4T5, F6T5, and F8T5. Generally used in vintage, older style clocks and signs that used a single fluorescent bulb for illumination. Email me if you have questions or want additional pictures. Please check out my feedback and other auction listings. Thanks