This PYREX® straight bore stopcock has a No. 3 PS stopper plug with a 3mm diameter bore. Stopcock sidearms have a 10mm O. D. The PS taper Teflon® plug fits into a micro-finish barrel. Freezing problems are reduced and greasing is eliminated. The very fine threads on the plug and nut let you "feel" the position of the plug. Sidearm seals are heavy and strong for greater durability and easier handling.