prongs are wrong size for sockets in my master bathroom

Although my contractor had told me that I needed MR 16 bulbs for the ceiling lights in my master bathroom, when the electrician came to put in the bulbs he advised me the I needed bulbs with very small prongs; and I need to return these bulbs because they don't fit in the sockets. I wasn't aware of the different size prongs of the MR 16 bulbs until my electrician finally came to replace the burned out bulbs.

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