= Spin projection
The <spin projection> is the component of a particle's <spin angular momentum> along a specified spatial direction. For the $z$ direction, an <eigenstate> of the <angular momentum operator> $S_z$ has measured value $m_s\hbar$, where $m_s=-s,-s+1,\ldots,s$ and $\hbar$ is the <reduced Planck constant>. For <spin one-half>, the two possible results are $+\hbar/2$ and $-\hbar/2$.
The direction belongs to the measurement arrangement: a state with definite $S_z$ generally has uncertain $S_x$. A <Stern-Gerlach experiment> separates the corresponding components through a spatially varying <magnetic field>. This is a component measurement, rather than a claim that the full <spin angular momentum> points along one of two classical directions.
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