[FTC]: Question On Material Legality

Our team wanted to try some things on our robot but found nothing in the FTC rule book about them. Can anyone help me clarify?

PVC end caps
springs (any size)

**PVC End Caps are NOT allowed:


Springs are ALLOWED BUT:

**The thing with springs is that FIRST wants you to make one out of the materials we are allowed to use. So I really don’t know how much effort you want to put in to actually make a spring.