Co-Axial quill assembly for dual fuel common rail system

A dual fuel common rail system (10) includes first and second common rails (16) fluidly connected to a fuel injector (12) by a co-axial quill assembly (18). Distillate diesel fuel at a first pressure moves from the first common rail (14) through a first fuel passage defined by a quill (30), through an inner tube (50) and into the fuel injector (12). Liquid natural gas a second lower pressure moves from the second common rail (16) through a second fuel passage (35) defined by the quill (30), through a space (45, 49) between the outer tube (40) and the inner tube (50), and finally into the fuel injector (12). The quill (30) is partially positioned in a block (20). First and second compression load adjusters (60) are threadably attached to the block (20) to adjust a compression load on the inner tube (50) and outer tube (40) to inhibit leakage of fuel from the tubes.