The fortieth anniversary is the Ruby Anniversary and all
gifts should be made of or consist of rubies. Ruby jewelry is the
usual gift for this occasion, and you will be limited to this
in your gift selection. There are just not many gifts made with rubies
that are not jewelry. There are other items that use rubies as
decorations, and you might consider looking at something like that.
Fortieth Anniversary Gift Ideas (Ruby):
Book on Rubies
The Modern 40th Anniversary Gift is also the Ruby.