Raw aluminum bulkheads CNC'd in house and work perfectly with modern DOT airline hose.  Threaded with 3/8" NPT.  We use these on all our chassis builds.  Can be Cerakoted upon request.
 
Sold as a set or also individually
Also available in 1/4" NPT
 
Set includes:
4x single bulkheads - one at each tire
2x double bulkheads - one at each tank valve