Reamers

The holy grail of framebuilder reamers for seat tubes is a solid spiral flute hand or chucking reamer. These are very hard to find in the fractional metric sizes common for seatposts.

Source for reamers

This is a good one:

KBC Tools & Machinary 1751 Sabre Hayward, CA 94545 (510) 732-5500 (800) 521-1740 KBCtools.com

27.2mm

Probably the most common size seatpost in the industry for steel bikes.

Size: Flute Length: OAL: KBC P/N: Price 1-1/16: 2-3/4: 10-1/2: 5-020-295: $37.40 (26.99mm for roughing) 1-3/32: 2-7/8: 11: 5-020-300: $37.40 (27.78mm reground to 27.2 for finishing)