Below are listed the nominal volumes and respective diameters for standard glass spherical "round bottom" flasks. The really little ones aren't exactly stock items; they are shown just for reference. There are small variations depending on the manufacturer; some are specified as "heavy wall", with larger outside diameters.

We receive them usually as blanks, that is, without finished necks, as shown in the photo on the right, and add to them as required. The photo below is a 1L 4-neck flask with a 45/50 female tapered joint, and three 24/40 female tapered joints.

Designing your glass parts around standard sizes can make a remarkable difference in your glassware cost.