Pentair has at least three configurations of peristaltic pumps for acid or chlorine dispensing, and multiple part numbers that contain the same Stenner #2 tubes. Ordered this item after working with Pentair tech support, but it was incorrect for my configuration. The package contains five Stenner #2 Santoprene tubes plus a single white plastic part -- no idea of its use. Tubes are 6.25" inside of the black plastic fittings. Return to SunPlay was not too bad: this was a stock item, so they accepted the return and I just had to pay for return shipping. (Still waiting for credit 5 days after package received at SunPlay's Connecticut facility.) Ended up purchasing a Pentair 522386 kit with cover, roller assembly, and tube to be sure of getting the correct tube, which it was for my "Blue" pump which I now know is a Stenner EC30 (it is 4" inside of the black fittings). Correct tube according to Stenner is an EC30C, but have not found a Pentair equivalent part number nor ordered the part yet to verify. Supposed to replace these yearly and was 15 months for me on my acid pump.