Tube Jointing Solutions

I'm looking for a solution to jointing some tube.

The Florida's roof rack is made up of ally tube which is jointed by plastic fixings.

So, for example, where one tube is joined across the end of another to form a 'T', the tube that forms the stem of the 'T' has a plastic fitting in the end of it.  The second tube that forms the top of the 'T' has a hole through which a screw goes and this screws into the plastic fitting in the stem of the 'T' holding them together. 
I want to replace all the fittings because some have cracked due to age and UV damage.

Any thoughts? I've had a good look at a number of companies that do pipe and tube pitting, but can't find anything where an insert goes in the tube and locks in place so another tube can be screwed to it.

I'll see if I can get some photos of that they typically look like.

Damn good idea that one.

Right, finally got my shit together and got some photos of what's on the Florida roof rack:

End of a tube:








Internal 'thing' that the fixing screws screw into:





It looks like I might need to make up some new tubing for the roofrack on the Flo (see my other post), so I need to make joints like this:













Edited by Chappy - 07 Apr 15 at 15:51

what about safety handrail fittings, you can get corners and T's in that stuff

There's useful now.

  failing that pinch 2 zimmer frames