| R&D Machine LLC Milling, Assembly | Murrieta, CA | MillingAssembly | - |
| Ram Aerospace Inc Milling, Turning, Laser, Waterjet, EDM, Grinding, Assembly · AS9100, ITAR | Brea, CA | MillingTurningLaserWaterjetEDMGrindingAssembly | AS9100, ITAR |
| Ramp Engineering Inc Milling, Turning, Swiss | Paramount, CA | MillingTurningSwiss | - |
| Rand Machine Works Milling, Turning, Bending, Welding | Fresno, CA | MillingTurningBendingWelding | - |
| Raw Machining Co Milling | Buena Park, CA | Milling | - |
| RC Industries Milling · ISO 9001, AS9100 | Anaheim, CA | Milling | ISO 9001, AS9100 |
| RDR Precision Tech Milling, Turning · ISO 9001 | Bakersfield, CA | MillingTurning | ISO 9001 |
| Redwood Machine Works, Inc Waterjet, Welding · ISO 9001, AS9100 | Oakland, CA | WaterjetWelding | ISO 9001, AS9100 |
| Responsible Metal Fab Inc Welding, Finishing, Assembly · ISO 9001 | Sunnyvale, CA | WeldingFinishingAssembly | ISO 9001 |
| Rieker Machine LLC Welding, Assembly | Carlsbad, CA | WeldingAssembly | - |
| Rincon Engineering Corporation Milling, Turning, Laser, Waterjet, Punching, Welding, Stamping, EDM, Finishing · ISO 9001, AS9100 | Carpinteria, CA | MillingTurningLaserWaterjetPunchingWeldingStampingEDMFinishing | ISO 9001, AS9100 |
| RivCut Milling, Turning, Bending, Metal AM · ISO 9001, AS9100, ITAR | Union City, CA | MillingTurningBendingMetal AM | ISO 9001, AS9100, ITAR |
| Rivera Solutions Inc Milling, Turning, Assembly | Gilroy, CA | MillingTurningAssembly | - |
| RJ Enterprises Milling, Turning, EDM · ISO 9001, AS9100, ITAR | Gardena, CA | MillingTurningEDM | ISO 9001, AS9100, ITAR |
| Robertson Machine Inc Milling, Turning | Santa Clara, CA | MillingTurning | - |
| Royal Coatings Grinding, Finishing | Simi Valley, CA | GrindingFinishing | - |
| Rozak Engineering, Inc Milling, Turning · ISO 9001, AS9100, ITAR, NADCAP | Fullerton, CA | MillingTurning | ISO 9001, AS9100, ITAR, NADCAP |
| Ruxco Engineering Inc Turning, EDM | Diamond Springs, CA | TurningEDM | - |
| S & H Machine, Inc Milling, Turning, Assembly · ISO 9001, AS9100, ITAR | Burbank, CA | MillingTurningAssembly | ISO 9001, AS9100, ITAR |
| S & S Commercial Fishing Equipment, Incorporated Milling, Turning, Welding | Roseville, CA | MillingTurningWelding | - |
| S R Machining, Inc Milling, Turning, Swiss, Welding, Casting · ISO 9001, AS9100 | Norco, CA | MillingTurningSwissWeldingCasting | ISO 9001, AS9100 |
| Sa Aerospace Inc Milling, Turning, Waterjet, EDM · ISO 9001, AS9100 | Sun Valley, CA | MillingTurningWaterjetEDM | ISO 9001, AS9100 |
| San Diego Precision Machining Inc Milling, Turning, Welding, EDM · ISO 9001, AS9100 | San Diego, CA | MillingTurningWeldingEDM | ISO 9001, AS9100 |
| San Jose Die Casting & Machining Corp Casting | Lincoln, CA | Casting | - |
| Santa Lucia Manufacturing, Inc Milling, Turning, Grinding | Atascadero, CA | MillingTurningGrinding | - |
| SDS Engineering Milling, Turning, Grinding · ISO 9001 | Sun Valley, CA | MillingTurningGrinding | ISO 9001 |
| Serrano Industries, Inc Milling, Turning, Swiss, EDM, Grinding · ISO 9001, AS9100 | Santa Fe Springs, CA | MillingTurningSwissEDMGrinding | ISO 9001, AS9100 |
| Sharp Dimension Inc Milling, Turning, Bending, Welding, Grinding, Finishing, Assembly · ISO 9001, ITAR | Fremont, CA | MillingTurningBendingWeldingGrindingFinishingAssembly | ISO 9001, ITAR |
| Sheet Metal Specialists (SMS Fabrications, Inc.) Bending, Laser, Welding, Waterjet · ISO 9001 | Riverside, CA | BendingLaserWeldingWaterjet | ISO 9001 |
| Si Aerospace Inc Milling · ISO 9001, AS9100, ITAR | Van Nuys, CA | Milling | ISO 9001, AS9100, ITAR |
| SJC Precision Inc Milling, Laser, Punching, Welding, Stamping, Grinding · ISO 9001, ITAR | Milpitas, CA | MillingLaserPunchingWeldingStampingGrinding | ISO 9001, ITAR |
| Snowline Engineering Laser, Waterjet, Welding, Finishing · ISO 9001, AS9100, NADCAP | Cameron Park, CA | LaserWaterjetWeldingFinishing | ISO 9001, AS9100, NADCAP |
| Sonoma Industries Inc Milling, Turning, Swiss · ISO 9001, AS9100, ITAR | Bell Gardens, CA | MillingTurningSwiss | ISO 9001, AS9100, ITAR |
| Southwest Greene International Inc Milling, Turning, Stamping, Metal AM, EDM | Oceanside, CA | MillingTurningStampingMetal AMEDM | - |
| Specialty Precision Machining Milling, Turning, Laser · ISO 9001 | Stockton, CA | MillingTurningLaser | ISO 9001 |
| Stines' Machine, Inc Milling, Turning · ISO 9001, ITAR | Vista, CA | MillingTurning | ISO 9001, ITAR |
| Superior Jig Inc Milling, EDM · ISO 9001, ITAR | Anaheim, CA | MillingEDM | ISO 9001, ITAR |
| Surfacemode, Inc Milling · ISO 9001, AS9100, ITAR | San Diego, CA | Milling | ISO 9001, AS9100, ITAR |
| Swiss Screw Products Inc Milling, Turning, Swiss, Grinding, Assembly · ISO 9001 | Santa Clara, CA | MillingTurningSwissGrindingAssembly | ISO 9001 |
| Systomatic Milling, Turning, EDM | Union City, CA | MillingTurningEDM | - |
| Szabo Precision Milling, Turning · ISO 9001, AS9100 | Diamond Springs, CA | MillingTurning | ISO 9001, AS9100 |
| T & T Metals Milling, Laser, Punching, Bending, Welding, Finishing · ISO 9001 | Covina, CA | MillingLaserPunchingBendingWeldingFinishing | ISO 9001 |
| Tecma Milling, Turning, Welding, Waterjet, EDM, Stamping, Casting · ISO 9001, AS9100, ITAR, NADCAP | Sacramento, CA | MillingTurningWeldingWaterjetEDMStampingCasting | ISO 9001, AS9100, ITAR, NADCAP |
| The Champ Company Welding, Assembly | Campbell, CA | WeldingAssembly | - |
| TL Machine, LLC Milling, Turning · ISO 9001, AS9100 | Garden Grove, CA | MillingTurning | ISO 9001, AS9100 |
| TM Industries Inc Milling, Welding | Santa Clara, CA | MillingWelding | - |
| Tomi Engineering, Inc Milling · ISO 9001, AS9100, ITAR | Santa Ana, CA | Milling | ISO 9001, AS9100, ITAR |
| Top Precision Milling, Turning, Assembly · ISO 9001, ITAR | San Luis Obispo, CA | MillingTurningAssembly | ISO 9001, ITAR |
| Topnotch Quality Works Milling, Turning · ISO 9001, ITAR | Pacoima, CA | MillingTurning | ISO 9001, ITAR |
| Total Concept Enterprises, Inc. Milling, Turning, Bending, Welding | Fresno, CA | MillingTurningBendingWelding | - |