Caulk or Woodfiller for this? Pics!

[goldpendant]

Anyone know whether this stair spindle needs caulk or woodfiller?

@pigletjohn

And the pic!

It's rather a loose fit.

I think there will be some movement, which would crack a rigid filler.

As you're going to paint it, I suppose caulk, but caulk shrinks and sinks over time, so for a big hole, fill it near the top for now, and then you can top it up after it's shrunk. Or when you paint it the second time in a few years.