  Understanding the origin of transverse single-spin asymmetries is a
long-standing challenge in strong interaction physics. Recent precise
measurements of the azimuthal distribution of charged pions in jets from STAR
have shed new light on the spin momentum correlations within the Transverse
Momentum Dependent (TMD) formalism. This measurement, particularly sensitive to
the Collins effect, correlates the quark transversity with the Collins
fragmentation functions, elucidating the spin-dependent fragmentation process.
Moreover, similar measurements involving kaons and protons, which have unique
quark compositions, provide vital insights into the flavor-dependent spin
dynamics of the parton distribution functions and fragmentation functions.
These studies are crucial for developing a more comprehensive understanding of
nucleon spin structure. In these proceedings, selection of the recent Cold QCD
STAR results are presented, focusing on the asymmetries for charged kaons and
protons in jets from transversely polarized $pp$ data at $\sqrt{s}$ = 200 GeV.
