When choosing a runner, the option equals as follows: 272-M-9 = Blade Size 272- Medium Rocker - 9mm Hollow. We offer runners in following sizes S, M & L: 264 (9-15), 272 (9-18), 280 (9-18), 288 (9-18). - Runner (blade) are made of a special glass fiber resin, which is tenacious down to lowest temperatures, provides optimum elasticity and doesn't break. - Locking disks enable blade replacement in a minute. - Blade system with excellent thermal qualities. - Choice of rocker styles (Short (S), Medium (M) and Long (L)) - Choice of hollow (radius) 9mm, 11mm, 13mm, 15mm and 18mm. - T-Blade runners last 5 times longer than 5 sharpenings of a conventional blade meaning LESS SHARPENING!