Standard I.D. can be reamed to larger sizes to fit a wide array of blank diameters and are a standard 25.4mm (1") long.

GA12 - 11mm (.43") O.D. x 5mm (.2") I.D.
GA14 - 14mm (.55") O.D. x 5mm (.2") I.D.
GA16 - 15.3mm (.60") O.D. x 5mm (.2") I.D.
GA18 - 17mm (.67") O.D. x 7mm (.28") I.D.
GA18L - 17.7mm (.70") O.D. x 7mm (.28") I.D.
GA20 - 19.3mm (.76") O.D. x 10mm (.39") I.D.
GA22 - 21mm (.83") O.D. x 10mm (.39") I.D.
GA24 - 23mm (.91") O.D. x 10mm (.39") I.D.
GA26 - 25.3mm (1") O.D. x 10mm (.39") I.D.
GA28 - 28mm (1.1") O.D. x 10mm (.39") I.D.
GA30 - 29.5mm (1.16") O.D. x 10mm (.39") I.D.