I went to Home Depot and found these. Couple bucks each and they do the job for my 315 duratracs. Its in the plumbing section. Its a plastic reducer. I don't remember the exact hole size but you will know what it is when you see it.
2013 2 door Commando Green Sport, 2.5 Teraflex lift, Rancho 9000XL shocks, Teraflex Monster Track Bar, Teraflex Exhaust Spacers, Rancho Drop brackets, Northridge bolt kit, JKS Quicker Discos, 315-70R-17 Duratracs on Level 8 Strike 5's. ACE rock sliders, Rugged Ridge XHD front bumper w/storage ends and RR synthetic line winch. Cobra 75 CB and 4' firestick, LoD rear linked full width bumper.RR Snorkel, high, low and precleaner.