Thanks Pete............Do you use a 'notched' type tool to depress the round spring retainer  sufficient to slip the keepers in place? there is not much room for error and Ive already lost one of the keepers as it flew around my kitchen pinging off the pots and pans sort of Davy Crockett like<div>
</div><div>The disc rotates freely with a uniform feel of friction all the way thru a rotation, in other words, its only slight but it is consistent, I assumed its the tightness of this fit  that helps to form the sealing effect. With the retaining screw  just 'nipped' up sufficiently tight the disc rotates just the same. There doesn't appear to be any difference in resistance with screw removed or fitted.</div><div>
</div><div>Regards Bob</div>