Length, watts, and retrofits for linear lamps.
The R7s base is standard: the critical dimension is the length (e.g., 78 mm or 118 mm). Check the length of your existing bulb.
Check the maximum wattage allowed by the lamp holder and decide whether you prefer halogen or LED retrofit bulbs.
If you're not sure, send us a photo of the light socket, and we'll tell you the correct part number.