Problems with poor threads radiator tappings

[LouiseSJPP]

I have bought seven aluminium CH radiators and find in all of them I can get the 1" bushes and rad tails in one side of the rad but not the other. The 'other' side, the LH side on all rads seems to be cross-threaded: the bush or rad tail starts to go in on a slant and cannot be straightened. It binds almost straight away.
Here's the kicker: one of the seven rads is a different make than the others and has the same fault, so the rational explanation of a manufacturing problem on a batch goes out of the window.
I'm tearing my hair out over this, totally baffled. Any ideas?

 

[LouiseSJPP]

LH thread!!! Why?

 

[Exedon]

Some designer rads have rh bushes for one side of rad lh for other.
Rad sections are made like that for assembly they use a lh/rh nipple that as its tighten pulls the section together.

 

[oldbuffer]

1. Its a (non-universal) engineering convention that threaded fittings with a left hand thread have a shallow groove cut into the hexagon part.
2. See if any of the bushes have such a groove, and try them in the left hand side of a radiator, obviously turning anti-clockwise facing the radiator end on.
3. I would expect all the radiator tails to have normal threads.
4. If none of the bushes have left hand threads, you need to get onto the supplier. They are also available on-line.