In article ,
harry writes:

I hope you're not just screwing it in by hand. There are often lugs
inside the tailpipe that are engaged by a special tool to screw the
fitting home. (Though some have internal/external hexagons.) Obviously
you won't have a tool but usually a big screwdriver can be found to
fit & then use an adjustable spanner on the screwdriver.

My old (or rather, my dad's old) 1/2" rawlplug cold masonary chisel
is an absolutely perfect fit for all the internal key radiator tails
I've encountered.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]