As a rat owner myself, I have took a dedication to analysing and inspecting said behaviour. Through my life times work I have been able to come to certain conclusions of which I am most confident of. When I seen your message, I was delighted that a common rat owner was curious of rats and how they function. I believe through this that you have earned the right to gain access to knowledge of which I've gathered through my journey. I wholeheartedly believe without a shadow of doubt that it would take approximately 4 rats to screw on a lightbulb.
Of course, this conclusion would come under the assumption that said rats would be rats of average health with no implications of limbs or cracked teeth. You would have one rat sit under the bulb, holding the weight of the bulb under the spinal area while the second rat would be stood on two feet with the other two limbs holding the bulb into a position to the connector. With those two roles fulfilled, it would be the task of the other two rats to be able to rotate the bulb the correct direction in order to complete the instillation of said bulb.