Margaret, that quote looks like it is from
Pulling a Trailer Safely, from the Ontario Ministry of Transportation, which looks like some good information.
For anyone interested in the nitty-gritty details, the same site links to Ontario's
Highway Traffic Act, R.S.O. 1980, c. H.8. The applicable section appears to be
s 80, which says nothing about the type of hook. I couldn't find anything in the
Statutes and Associated Regulations - Highway Traffic Act which adds to that section.
My utility trailer needed new chains, so I bought a set with hooks that have spring catches on them. My
Boler is still using what I assume are the original chains (rusty brown but solid) with an unusual (to me) configuration: the chain is passed through the attachement loop of the hitch, doubles back on itself, and connects at the desired point with a hook that looks like one of those wire puzzles (and it just as frustrating when you first use it). It is slow to use, but adjustable to any length (by choosing which link to hook back to), and seems quite secure.