| 511 | Oyster Sauce Manufacturers | Company Product |
| 512 | Oxygen Gas Distributors | Company Product |
| 513 | Oxygen Level Sensors | Company Product |
| 514 | Oxygen Gas Manufacturers | Company Product |
| 515 | Oxygen Dissolved Level Meters | Company Product |
| 516 | Overload Relays | Company Product |
| 517 | Overhead Projectors | Company Product |
| 518 | Oxalic Acid | Company Product |
| 519 | Overhead Cranes | Company Product |
| 520 | Overalls | Company Product |
| 521 | Ovens | Company Product |
| 522 | Output/Input Modules | Company Product |
| 523 | Orp Sensors | Company Product |
| 524 | Oscilloscope Probes | Company Product |
| 525 | Oscilloscopes | Company Product |
| 526 | Orifice Plates | Company Product |
| 527 | Orifice Flanges | Company Product |
| 528 | Oriental Goods Retailers | Company Product |
| 529 | Organs Agents & Distributors | Company Product |
| 530 | Optical Fibre | Company Product |
| 531 | Organic Food | Company Product |
| 532 | Organisation Charts | Company Product |
| 533 | Opticians | Company Product |
| 534 | Optical Measuring Systems | Company Product |
| 535 | Optical Goods | Company Product |
| 536 | Optical Shops | Company Product |
| 537 | Open Plan System Office Partition | Company Product |
| 538 | Operable Walls | Company Product |
| 539 | Operate & Relocatable Walls | Company Product |
| 540 | Open Side Planing Machines | Company Product |