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A screw dislocation is a crystal line defect whose Burgers vector is parallel to the dislocation line. Atomic planes around it have a helical arrangement, rather than the extra-half-plane geometry associated with an edge dislocation.

Its motion permits crystal slip. Because several planes can contain the same line and Burgers vector, screw segments can sometimes change their glide plane by cross-slip, with the actual possibility depending on the crystal and defect structure.

An FCC partial dislocation with Burgers vector $a⟨112⟩/6$ lying in a close-packed $\{111\}$ plane. Two suitable Shockley vectors can sum to an FCC perfect vector $a⟨110⟩/2$.

A sessile partial junction associated with intersecting stacking faults. A typical FCC resultant has vector $a⟨110⟩/6$. Its Burgers vector and junction line can define a plane outside the ordinary $\{111\}$ glide family.