Working with bikes can drive you nuts, if you look at things logically as a mechanic. Nothing much in the industry is standard, when it comes to sizing.
On the handlebars, for instance, it's not unusual to find three different sized bolts. The stem will have a 6mm bolt camping the bar, and 2.5mm bolts clamping the stem to the steerer. The brake levers will be 5mm, while the shifters are 4mm (or 2.5mm if GripShift twist grips).
Seatposts are sized from 25mm to 39mm in diameter...in 0.2mm increments, and come in lengths varying from 200mm to 425mm. Front hub cones are 13mm (sometimes...other times they are 15mm), while rear cones are 15mm (unless they are 16mm).
There are three different sizes of spoke nipples! Four sizes of headsets, not including the tapered versions which are gaining popularity.
And, let's not even get into French, Swiss, Italian and English bottom brackets (plus the new over-sized bottom brackets and the pressed-in Gary Fisher and Merlin versions, from the past).
Chainrings come in 3, 4 and 5-bolt patterns, with each number of bolts having more than one center-to-center measurement, depending on the manufacturer (or the model, in the same manufacturer's line).
Pedals come in 1/2" and 3/4" spindles, with English and (rarely) French thread. Let's ignore the over-sized Shimano Dura-Ace spindles of the early 90s. Please.
There are a half-dozen different bottom bracket spindle-to-crank interfaces floating around.
Every hub/rim combination takes a different length of spoke to lace up, in the same configuration (3-cross, 2-cross, radial, etc.).
Chains come in 4 different widths, depending on the cogsets they are used on. BMX chains and freewheels each come in three different widths.
Every suspension fork and rear shock takes a different tool kit to maintain it, and/or repair it.
Shimano shifters will not work on Campagnolo drivestrains or SRAM drivetrains, and vice-versa.
There are two different versions of Campagnolo 9-speed. The shifters and derailleurs are not compatible between them.
It goes on and on.
In the mid 90s, Cannondale teamed up with the guys at Magic Motorcycle and came out with a prototype mountain bike on which every bolt was a 5mm Allen. One wrench would turn every bolt on the entire bike.
It never went into production. Just like the Chevy EV1 electric car.
Who killed the Standard Bicycle?