Part Number: 186000304. Waters offers a selection of cap, septum, and assembled cap/septum for various vial sizes. The range of septum material is limited to PTFE, silicone / PTFE, and polyethylene septumless caps. Blue, 12 x 32mm Snap Neck Cap and preslit PTFE/silicone Septum, 100/pkg. Part Number: 186000304.