This is a pair of "L-Out" pieces from the Spiral Group of puzzles. Spiral Group pieces combine in many ways to form 4x4x4 cubes. Eight total pieces are needed to make a cube. It's possible to make cuebes with as many as eight different pieces, but pairs make the most common solutions. Check the compatibility chart below for which other pieces you might want to use.

L-Out Compatibility:
L-Z ---------- G
LS ---------- O
L-Out ------- G
Little-j ------ G
Arc ---------- G
Double-L - G
L-v ---------- X
C-N --------- X
Hook ------- O
Z-Tip ------- O
Helix ------- H
Loop ------- X

G = Forms a cube with Good interlock
O = Forms a loose Or unstable cube
X = Can't make a cube without other pieces added
H = Assembles into two Half-cubes
This chart is for basic mix of four pieces of each kind. Note that the piece is also matched with itself.