Hi zzw

I agree your point is correct.
But there are some practical aspect. Say we want exact 2 mm gap in particular support but at site it will not be possible to make that exact gap with common standard support. Gap at site may be 1 mm or 3mm.
Point is that we should not make a piping system where gap tolerance will seriously affect the system.
Some system still we require to maintain exact gap. Rigid strut is special piping attachment that can ensure exact zero mm gap. We can use it in critical system.