Knuckle · Round tip — despite the name, from the Round — from the Round primal.
Confusingly named — the sirloin tip is actually the front of the leg, not the sirloin. The peeled knuckle breaks into several lean sub-muscles that make excellent value steaks, stir-fry, kebabs, and rotisserie roasts.
What It's Called
United States: Sirloin tip, Round tip, Knuckle
Australia: Knuckle, Round
United Kingdom: Thick flank, Knuckle
How to Cook It
Rotisserie: Self-basting rotation suits its leanness.
Stir-fry / thin-cut: Slice thin against the grain, cook fast.