Replacement part sizing

marchant

Okay, this feels like a daft question, but how are bike parts measured? For example, stem length; are they measured in terms of overall length (black), or from mid-point to mid-point (red), or from the nearest point of the steerer tube to the nearest point of the bar? And what about seatpost clamps? Here's an example to try and illustrate my quandry;



Help me please, it's driving me crazy

always_tyred

Red.

Seatpost clamps measured in relation to the seat post diameter they are intended for use with.

Frames, however, seem to be measured between any two random nodules positioned anywhere on the bike.

nicklouse

stems are center to center. cranks C to C, seat posts diameter of the post, seat post clamps the diameter of the seat tube (frame).

Frame sizes ask the producer as as said above they vary.