They also have specific pen models mentioned in a table, with pen sac sizes identified.
This guide is pretty good, and I have found it to work with most of the replacements I have done, and generally agrees with what various people have recommended. The good part is that it gives you a formula you might consider using on any pen - especially those interesting unknown makers sometimes encountered.
Hope this helps...
Pen Sac Sizing
While every effort has been made to provide as comprehensive as possible a listing of suggested ink sacs sizes, no catalog can contain all the vintage pen models which have been produced and which are now finding their way into the hands of collectors. As a result, by studying the relationship between pen barrel diameter and ink sac sizes, we have derived formulae which should allow for a very close estimate of the original sac size for models not listed. All that is necessary is a good measurement of the inside diameter of the pen barrel. When inside barrel diameter is measured to the nearest hundredth of an inch, the OD of the sac needed ( in 64ths of an inch) can be calculated as follows:
For PARKER PENS: Sac Size (OD) = Inside barrel diameter x 56
For SHEAFFER PENS: (lever fillers only) Sac Size (OD) = Inside barrel diameter x 50
For WAHL-EVERSHARP PENS:( Except Skylines) Sac Size (OD) = Inside barrel diameter x 59
For WATERMAN PENS: Sac Size = (Inside barrel diameter x 72) - 6.5
As an example, the inside barrel diameter of a full-size Sheaffer flat-ended Lifetime pen measures .40 inches. Using our formula for Sheaffer Pens the ID(.40) x 50 = 20. The repair manual actually lists a number 20 sac as the correct size.
For pens other that the BIG FOUR, the formula given for Sheaffers should provide a very good estimate of the sac size required. The fit may be slightly loose, but quite acceptable.
As we acquire more information concerning other pen companies, we will attempt to update this catalog and make it available to you.
Good Luck with your repairs.
[Info from the pen sac company - http://www.pensacs.com/index.html]
Edited by Gerry, 30 January 2005 - 01:58.