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.