SIZE 19 LATEX SAC
I bought size 18, 19, and 20 ink sacs for a 1950's vintage Watermans lever fill fountain pen with a 9mm nipple on the grip section. I didn't know which would fit best. The 18 was the best fit for the pen, but the quality of the others are good too. I bought 3 of each and the unused ones went into my supplies drawer. The 19 and 20s are the right size for my 1930's vintage Salz Brothers and Stratford fountain pens.