3/8" barb x 1/8" NPT brass fitting for filler neck vent lines. This fitting is ideal for applications where the original fuel system used a vented cap but lacks a dedicated tank vent—common in early vehicles like 1964–1970 Ford Mustangs and many 1950s–60s models.
 
Installation is simple: remove the filler neck, drill and tap it to accept this fitting, and install it to create a proper vent path. Then route the vent line to the Vapor Trapper™ and out to the atmosphere. Be sure to replace the fuel cap with a non-vented version for optimal performance