butyl tape comes in different shapes also. round and square. i like the round better because it is easier to get it to squish down and seal. if you are not sure what size to use, install mldgs. without glass. measure how much room is left, subtract thickness of glass. use tape that is just slightly thicker. windshields made today are alot thinner than the 60's/70's. same with tempered. (backs and sides) you never want to use silicone between rubber and metal. most silicone is acid base, thats why it smells like vinegar. however it is acceptable/ recommended to use silicone between the rubber and glass. it seals and will easily come loose in the future if needed. just lay a small bead, 1/8" before zipping gasket. zip gasket, spray with glass cleaner, scrape gently with razor. use urethane or the gooey butyl stuff between rubber and metal. clean up with mineral spirits. also not a bad idea to tape off painted surfaces. dennis