DV,
Your photgarphs may be misleading you.
Threaded they may be - but are they sealed and/or locked?
There are many ways of locking joints, even mere threaded Plugs and Sockets.
I'm afraid you'll have to do better than quoting a photgarph from "Training Notes in 2006".
I assume from your location that you are amongst Bristols 'finest'. If so, find someone who can back up your proposition rather than wildly speculate on some unpublished picture from more than 5 years ago.
I have a picture of Fairies at the bottom of my garden...
...we were having a BBQ.