1" steerer has I.D of 22.2mm 1 1/8" steerer has I.D of 25.4mm (1") 1 1/4" steerer has I.D of 28.6mm (1 1/8")
Steerer = the fork's steering column in your post. The original sentence refers only to the stem, so I read steerer as the stem's fork clamp size, which is the usual denomination.
@Lolo started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
1" steerer has I.D of 22.2mm
1 1/8" steerer has I.D of 25.4mm (1")
1 1/4" steerer has I.D of 28.6mm (1 1/8")