I live on my own & only want to use o of the ceramic filters a a time but I am forced to use the two filters at once because there are two holes & you haven’t supplied me with a blanking of nut & bolt. Also, the nuts on the filter units are plastic, so it is easy to jump thread & damage the plastic thread whilst tightening the filter to the hole in the glass. I know you cannot tighten too much where you have a hole in glass but a plastic nut on a plastic thread doesn’t allow you to get enough pressure on the compressible washer to get a good seal, there is just enough pressure to get a seal and it feels very fragile like the plastic nut could jump a thread & then you’ve lost your pressure & the seal. We need stainless steel nuts to go on the throw away plastic threads on the throw away ceramic filter units. Disappointed in the low-level engineering for the high price of these products.