25.4 mm seatpost (25.4 mm)
Which frames use a 25.4 mm seatpost, and how it differs from the sizes either side of it.
Published dimensions
| Diameter | 25.4 mm (1 in) |
|---|---|
| Designation | 25.4 mm |
| Typical frames | BMX, older utility and one-piece-crank frames with a 1 in seat tube |
Used on: BMX, older utility and one-piece-crank frames with a 1 in seat tube.
25.4 mm is the old 1 in American size, still seen on BMX and some utility frames. It is much smaller than a road 27.2 mm, so the two are not interchangeable, and a 25.4 mm post in a wider tube will slip.
Frames and related seatpost sizes
27.2 mm seatpost27.2 mm30.6 mm seatpost30.6 mm30.9 mm seatpost30.9 mm31.6 mm seatpost31.6 mm34.9 mm seatpost34.9 mmBSA bottom bracket shellthe frame's other threaded interface
SOURCES: Sheldon Brown, Seatpost Size Database · BikeGremlin, Seatpost diameter sizes (standards)