Models of many scales

555 Timer

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Wikipedia summary:

The 555 timer IC is an integrated circuit used in a variety of timer, delay, pulse generation, and oscillator applications.
It is one of the most popular timing ICs due to its flexibility and price. Derivatives provide two (556) or four (558) timing circuits in one package.

Mountain bike

Dimensions:

Wikipedia summary:

A mountain bike (MTB) or mountain bicycle is a bicycle designed for off-road cycling (mountain biking).
Mountain bikes share some similarities with other bicycles, but incorporate features designed to enhance durability and performance in rough terrain, which often makes them heavier, more complex and less efficient on smooth surfaces.