In this website, we credit the people involved in the understanding of these codes. (Naturally, for information provided by others, such as for the Campagnolo and Williams codes, the original source should be cited.)Ben writes: "Brakes and brake levers often have date codes on them.Weinmann and Dia-Compe calipers usually have codes on the back of a caliper arm.Some bike parts have a date code cast or stamped into the piece.This clearly is when the component was made and not when the bike was made, but unless the component or bike manufacturer had lots of stock lying around in inventory, the date should be a fairly good indication of the year of the bike.
Even those equipped with Suntour Superbe components usually had SR seatposts.
Swaps can take place early in the life of a bike as the proud new owner upgrades to new or used components of higher quality.
Swaps also can be made as the bike falls out of favor, or is being sold, where the higher quality components are traded for lower quality ones that the owner had onhand.
Seatposts are marked with outside diameter, also in mm.
For old Treks, 27.2 is the most common, but for other bikes the diameters can range from 25mm to 33mm.