Pinnerite wrote:

I have some cast aluminium garden chairs.
The screw holding one of the arms got loose and I forgot to tighten it.

Yesterday the top of the arm snapped off, leaving the screw in place.

I have the arm and the s,mall piece that snapped off.
The ends are clean and thankfully not shiny smooth but bright non-the-less.

I have gorilla clue, araldite and regular superglue.

Will any of those be OK or should I buy something else?

With the forces likely on an arm against its mounting bolt I think there
is zero chance of glue working. Either get someone to weld it or put a
long steel strap around the end going at least a few inches up the arm
on both sides and screwed, to reinforce the glued joint. If you don't
mind what it looks like.
--

Roger Hayter