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ISO
The International Organization for Standardization. This is an international agency that is active in trying to rationalize bicycle design to make parts interchange more easily among bicycles made in different countries. Most ISO standards are compatible with British standards. These standards include:
- 1" x 24 tpi headset thread
- 1" (25.4 mm) handlebar/stem clamp diameter
- 1.375" x 24 tpi bottom bracket thread (left-hand on the fixed cup)
- 1.375" x 24 tpi freewheel thread
- 56 TPI spoke thread
- 1 mm axle thread
In the case of tires and rims, the ISO adopted the E.T.R.T.O. system, the modern system for designating tire and rim sizes, based on Bead Seat Diameter. This is explained in detail in my article on Tire Sizing.
Since the standards were adopted, innovation and product differentiation have resulted in a proliferation of parts that no longer conform to them, because these parts are designed entirely differently. This has occurred with spokes, headsets, bottom brackets, chains, sprockets...
