This cylinder plug is made for straight thread high pressure cylinders.  It has a wide lip to cover the entire flange area of the cylinder and has a stepped down area to cover the area where the O-ring resides.  It is great for aluminum cylinders.  It has two pull tabs for easy removal.  It comes in three different colors.  Part Numbers:  ACM 428 (Black), ACM 434 (Red), and ACM 435 (Green).