What's the diameter of the bucket in a Bucket Light/Yardblaster/NEMA Head?
I want to be able to fit a big CFL inside, and see how compact bucket lights actually are. I would also like to know the dimensions of other parts of it.

Bucket and NEMA lights are the same thing, but Yardblasters are a different dimension than NEMA heads. 

I'm looking for the diameter of the top and bottom of the bucket in inches. I don't have any BT shape bulbs to compare.

Because I have a number of different NEMA or bucket yard lights that I noticed a slight difference, the question made me respond.

My older heads have a 6" diameter opening. These are the two in front.
The newer heads have a 7" diameter bottom. The 4 on the wall are of this type.

I like smaller ones better.