Originally Posted by
2manybikes
... sometimes your need to take the crank off, and that requires a special tool.
That is a 'one piece' (Ashtabula) style crank. It is an outdated design generally only found on the least expensive modern bikes. The one advantage it has (besides low cost) is that is can be fully disassembled with no specialized tools - IIRC you only need a large adjustable wrench.
https://www.sheldonbrown.com/opc.html