<https://www.hobbyhomebrew.com/product/10-5-solid-rubber-stopper-53mm-top-45mm-bottom-white-gum-from-vintage-shop/#product>
<http://schema.org/description>
"#10.5 Solid Rubber Stopper, made in Canada by our friends at Vintage Shop.  Fits holes roughly ~45-50mm.  This Problem Solving size is somewhat non-standard, be sure this the size you need. (See Below and Size Chart).   Safe, food-grade, BPA-free, injection-molded rubber that provides an excellent grip and air-tight seal on glass and PET surfaces even when wet. Not for laboratory use. Maximum Temperature: 158F (70C)."
<https://www.hobbyhomebrew.com/product/10-5-solid-rubber-stopper-53mm-top-45mm-bottom-white-gum-from-vintage-shop/>