These fittings are included in our 2nd generation Powerstroke kit ('99-'03) and used to adapt the highpressure fuel filter to threaded barbed fittings.  we have also used these adaptors in custom turbo applications for oil feed lines.
Made in the USA from 6061 aluminum, this kit includes one fitting with a 5/16" barb and 10mm-1 female thread, the other fitting is 10mm-1 male thread and 1/8"NPT.