This assembly has 2 each 38 mm bottle caps connected to each other with 1/4 inch OD tubes. The Bottle Cap Assembly is, Polypro with Stainless Steel Band,. There is a filter on the dip tube in the first bottle, to transfer liquid from the first bottle to the second bottle passing it through the filter on the dip tube of the first bottle. There is a 1/8 inch OD tube that brings gas pressure to the first bottle and there is a 1/4 inch OD tube that brings liquid from the second bottle to the instrument.