Dave Plowman (News) wrote:

A 2mm wall thickness ain't going to give much of a thread for M5 bolts.

It's what's specified by the manufacturer of the tube and brackets,
nonetheless.

The usual way would be to weld in bosses to increase the thickness. As a
rule of thumb, you want about the same thread length as the diameter as a
minumum.

The balluster posts are available pre-cut/drilled to take the glass
clamps, so I've purchased those, which are M8 tapped, I don't think they
use thread inserts for them.