This large Bubble FS109 type rectangle bubble shaped head type gasket was widely used on the popular Folding Sliding Door Timber version bi-fold door systems (FSD). The gasket has a ribbed v shaped insert to the bottom which is purpose made to push snugly into a purpose made groove machined into the timber profile to allow it to fit snugly and securely in place to ensure the gasket is held upright so the folding leafs provide a tight weather seal to the bifold doors.
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