This entire assembly is a great way to order one of the very few “wear & tear” parts of the Watermatic 300 & 1000 units. It also is used on the Watermaster 54, 54D, 90, 96, 600, 1200, Cattlemaster 480, 840, 1440, 10T and on the Thriftyking CT2 & CT4. It can be an extra part you order along with a new waterer and hold in reserve, or it can be a part you order a few years later when it might actually be needed. Any one part of this assembly can also be ordered as well, but you need to check the parts view of your model of waterer in our parts section to determine those individual parts or contact us to do it for you. It will be shipped with the red valve suitable for pressures of 40-60 psi.  That is the usual pressure found on residential homes in the country. If you would like a different valve, order the pieces separately by using the P-V link to get the part#’s, then use the P-O link to place your order – these links are found on the product page of your waterer.