| 66 | 6605 | Navigational Instruments |
| 66 | 6610 | Flight Instruments |
| 66 | 6615 | Automatic Pilot Mechanisms and Airborne Gyro Components |
| 66 | 6620 | Engine Instruments |
| 66 | 6625 | Electrical and Electronic Properties Measuring and Testing Instruments |
| 66 | 6630 | Chemical Analysis Instruments |
| 66 | 6635 | Physical Properties Testing and Inspection |
| 66 | 6636 | Environmental Chambers and Related Equipment |
| 66 | 6640 | Laboratory Equipment and Supplies |
| 66 | 6645 | Time Measuring Instruments |
| 66 | 6650 | Optical Instruments, Test Equipment, Components and Accessories |
| 66 | 6655 | Geophysical Instruments |
| 66 | 6660 | Meteorological Instruments and Apparatus |
| 66 | 6665 | Hazard-Detecting Instruments and Apparatus |
| 66 | 6666 | Historical FSC |
| 66 | 6670 | Scales and Balances |
| 66 | 6675 | Drafting, Surveying, and Mapping Instruments |
| 66 | 6680 | Liquid and Gas Flow, Liquid Level, and Mechanical Motion Measuring Instruments |
| 66 | 6683 | Historical FSC |
| 66 | 6685 | Pressure, Temperature, and Humidity Measuring and Controlling Instruments |
| 66 | 6689 | Historical FSC |
| 66 | 6695 | Combination and Miscellaneous Instruments |
