Same anatomical muscle group — the knuckle at the front of the round. Bola de lomo is the Argentine retail cut; sirloin tip / knuckle is the US–UK name. Same cut, different tradition.
Translation takeaway
These are near equivalents in the way butchers and cooks use them. If you can source either one, you're very close to the same result.
Keep Bola de lomo and Sirloin tip together in your notebook.
Names by country
| Country | Bola de lomo | Sirloin tip |
|---|---|---|
| 🇺🇸United States | — | Sirloin tip |
| 🇬🇧United Kingdom | — | Top rump |
| 🇫🇷France | — | Tranche grasse |
| 🇪🇸Spain | — | Babilla |
| 🇦🇷Argentina | Bola de lomo | — |
| 🇲🇽Mexico | — | Pulpa bola |
| 🇧🇷Brazil | — | Patinho |
| 🇮🇹Italy | — | Noce |
| 🇩🇪Germany | — | Kugel |