Thanks CarlS. Sorry for bad pictures and will take your advice.
Emike, those are wonderful pictures! I hate my pictures are bad, and I hate my base is in bad condition (flood land artifact). But just looking at your pictures, I'm thinking mine is a base for a 6-pounder, not 3.8. But because my artifact is in such poor condition, I'm not sure I could get decent measurements even with calipers. It just seems from your pictures my base looks smaller. If they never made bases for 6-pounders, then I guess I'll have to go with 3.8.