Step 1: Tighten BART's head in a bench vise on the "Flats" provided.
Step 2: Put barrel in upper. Slide barrel nut over barrel and finger tighten barrel nut to upper.
Step 3: Slide upper onto BART 2.0 until barrel extension locks onto the teeth
Step 4: Tighten barrel nut to upper with barrel nut wrench to specifications stated by handguard manufacturer.