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Frame tubing is generally standardized by external diameter to imperial dimensions in increments of 1/8 inch, which makes it a lot easier to standardize things like front derailleur clamps. Seat tubes therefore tend to have external diameters of 1 1/8” (28.6 mm), 1 1/4” (31.8) or 1 3/8” (34.9 mm). Handlebars are similar. Though there has been more variation ...


The dimensional differences have to do with purpose of the individual part. The seat post outside diameter has to match the seat-tube inside diameter.If you are asking why they didn't make it .2mm thicker it was a design decision. Based solely on an engineers experience or opinion. It may have been because they wanted a thicker wall on the seat tube or they ...


I disassembled two that were readily available, one on a Giant and one on a Specialized. Both use an M8 x 18mm. The 18mm length dimension did not include the head of the bolt. The total length was 24mm. I also noted both bolt heads were slightly shorter than industrial standard. Visually it looks like a bolt with a taller head would work but 1/2 head would ...


Looks to me like Shimano CI Deck gear indicators. They connect to the shifters with a little cable that pulls a dial to tell the rider what gear they're using. From the user's view:

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