"Standard" lamp knob replacement.
The hole size is for a 2-56 thread (as this size was the first knob I had to replace), but it can be drilled to larger sizes (I drilled and tapped another for 4-40 threads). Drilling and/or tapping may not be necessary, depending on the thread size of the lamp socket.
Designed using Sketchup 8 and printed in PLA on a Makerbot Replicator 2 using Makerware 188.8.131.52 "Standard" settings. For added strength, increase the infill.