Barrel Guide
Above is a rough list of common barrel materials used today in the Nerf Internet Community. Always choose which barrels fit your foam best, instead of finding foam to fit a specific barrel material. From general knowledge, you'll want your foam to be tight in your barrels for springers, and loose for "air" blasters.
All Part numbers are associated with McMaster.com
Disclaimer: These measurements are not exact. A lot of the materials specified vary greatly (ID) depending on a number of factors. It's always best to check them with a set of calibers to ensure the size.
(For copy/pasting part #'s)