Nuts and Bolts
Nuts and bolts are in your future. I try to keep the nuts and bolts on my bikes tight … if I don’t over time they loosen and fall off. Also, nuts and bolts on some components aren’t the best, over time corrode and need to be replaced. After a few years of riding I have some that definitely need to be replaced.
Finding good nuts and bolts isn’t easy … the best are a good grade of stainless steel and have nylon binders in the nuts or on the bolts.
A source that a recumbent/trike rider friend recommended is PowerOn Cycling. He buys most of his parts from them. I recently bought replacement idlers from them and can say they are quick and easy to work with. They definitely have some hard to find parts that most recumbent riders will need. They only show a few nuts in their online catalog but have more.
Another more complete source is Allen Fasteners. Ordering from they is more complicated because they sell all kinds of fastners and you will have to look through a lot more items to find what you need.
When in doubt about what you need talk with your local bike shop and buy from them.