Stair railing construction
 

At the salvage room of an antique store I saw some balusters. Some had a round tenon on the base; it makes sense how to use them.

But some has a round dovetail tenon on the base. Anybody know how these are used?

Also some had a rectangular tenon on the base; 2 of the faces were parallel; the other 2 taper inward at an angle like a dovetail. Anybody know how these are used?