ali tube is 12.7mm aka 1/2 inch
you need a 1/2 inch spring, however it don't bend very well as it right cheap & nasty shite compared to what it used to be....
So I doubt your going get 45°
1st result in google - https://www.ac-one.co.uk/tube-bending-springs-1281-p.asp
Post a picture of what your doing we can take the piss ?