Comparison : Item # 221-441-54, 5/16 Inch O.D. Tube Acetal Push-To-Connect Tube to Female Flare Straight Adapter
Item # 221-441-64, 3/8 Inch O.D. Tube Acetal Push-To-Connect Tube to Female Flare Straight Adapter
Item # 221-441-66, 3/8 Inch O.D. Tube Acetal Push-To-Connect Tube to Female Flare Straight Adapter