| Hoosier, Inc Turning · ISO 9001, ITAR, ISO 13485 | Corona, CA | Turning | ISO 9001, ITAR, ISO 13485 |
| HP Machine & Engineering Inc Milling, Turning, EDM | San Jose, CA | MillingTurningEDM | - |
| HPR Machine Milling, Turning | Vista, CA | MillingTurning | - |
| Hunt Enterprises Milling, Turning, Welding | Santa Ana, CA | MillingTurningWelding | - |
| Img Companies LLC Milling, Turning, Welding, Finishing · ISO 9001, AS9100 | Livermore, CA | MillingTurningWeldingFinishing | ISO 9001, AS9100 |
| Infiniti Manufacture Milling, Welding, Finishing | Corona, CA | MillingWeldingFinishing | - |
| Infinity Precision Inc Milling, Turning, Waterjet, Bending, Grinding · ISO 9001, AS9100 | Simi Valley, CA | MillingTurningWaterjetBendingGrinding | ISO 9001, AS9100 |
| Infocus CNC Machining, Inc Milling, Turning, Swiss · ISO 9001, AS9100 | Fountain Valley, CA | MillingTurningSwiss | ISO 9001, AS9100 |
| Inland Marine Industries Inc Milling, Turning, Waterjet, Punching, Bending, Welding, Grinding, Finishing · ISO 9001, ITAR | Hayward, CA | MillingTurningWaterjetPunchingBendingWeldingGrindingFinishing | ISO 9001, ITAR |
| Inno Tech Manufacturing Inc Milling, Turning, Laser · AS9100 | San Diego, CA | MillingTurningLaser | AS9100 |
| Innovation Alley Milling, Turning, Bending, Welding | Fresno, CA | MillingTurningBendingWelding | - |
| InSight Manufacturing Milling, Turning, Welding, Forging, Assembly | Murphys, CA | MillingTurningWeldingForgingAssembly | - |
| Inspirnetics, Inc Milling, Turning | Rancho Cucamonga, CA | MillingTurning | - |
| Inventery Precision Milling, Turning, Swiss, Finishing, Assembly · ISO 9001, AS9100, ITAR, CMMC | Pasadena, CA | MillingTurningSwissFinishingAssembly | ISO 9001, AS9100, ITAR, CMMC |
| Ipanel Systems Inc Milling | Santa Clarita, CA | Milling | - |
| J & R Machine Works Milling, Turning · ISO 9001, AS9100 | Lancaster, CA | MillingTurning | ISO 9001, AS9100 |
| J and J Custom Machining L.L.C Milling, Turning · ISO 9001 | Camarillo, CA | MillingTurning | ISO 9001 |
| J. I. Machine Co., Inc Milling, Turning, Swiss · ISO 9001, AS9100, ITAR | San Diego, CA | MillingTurningSwiss | ISO 9001, AS9100, ITAR |
| Jack West CNC, Inc Milling, Turning, EDM | Chula Vista, CA | MillingTurningEDM | - |
| Jaffa Precision Engineering Inc Milling, Turning, Swiss, Welding, Grinding, Finishing · ISO 9001 | Riverside, CA | MillingTurningSwissWeldingGrindingFinishing | ISO 9001 |
| Jars Inc Milling, Waterjet, Bending, Welding, EDM, Grinding, Finishing | San Fernando, CA | MillingWaterjetBendingWeldingEDMGrindingFinishing | - |
| Jerry's Welding & Machine Welding | San Diego, CA | Welding | - |
| Joels Machine Shop Inc Milling, Turning, Grinding | El Monte, CA | MillingTurningGrinding | - |
| Johnson Manufacturing Milling, Turning, Grinding · AS9100 | Huntington Beach, CA | MillingTurningGrinding | AS9100 |
| Justified Performance LLC Laser, Bending, Welding, Finishing, Assembly · ISO 9001 | Rocklin, CA | LaserBendingWeldingFinishingAssembly | ISO 9001 |
| K-V Engineering Inc Milling, Turning, Punching, Welding | Santa Ana, CA | MillingTurningPunchingWelding | - |
| Kaydek Machining, Inc Milling, Turning, Finishing · ISO 9001, AS9100 | San Jose, CA | MillingTurningFinishing | ISO 9001, AS9100 |
| KD Precision Machining Inc Milling, Turning · AS9100 | Corona, CA | MillingTurning | AS9100 |
| Kern Steel Fabrication Inc Bending, Welding · ISO 9001 | Bakersfield, CA | BendingWelding | ISO 9001 |
| KNM Manufacturing Inc Bending | Fremont, CA | Bending | - |
| Krisalis Precision Machining Milling, Turning | San Andreas, CA | MillingTurning | - |
| L & R Machine Inc Milling, Turning, Grinding | Rancho Cucamonga, CA | MillingTurningGrinding | - |
| L.F. Industries, Inc Milling · ISO 9001, AS9100 | Carlsbad, CA | Milling | ISO 9001, AS9100 |
| Lam Precision, Inc Milling, Grinding · AS9100 | Anaheim, CA | MillingGrinding | AS9100 |
| Langill's General Machine Inc Milling, Welding | Sacramento, CA | MillingWelding | - |
| Laserbend, LLC Laser, Bending, Welding, Finishing | Tujunga, CA | LaserBendingWeldingFinishing | - |
| Lean Manufacturing Group LLC Milling, Turning, EDM · AS9100, ITAR | Valencia, CA | MillingTurningEDM | AS9100, ITAR |
| LNP Machining Milling, Turning, Welding, Finishing · ISO 9001, AS9100, ITAR, ISO 13485 | San Jose, CA | MillingTurningWeldingFinishing | ISO 9001, AS9100, ITAR, ISO 13485 |
| LNT Machining Inc Milling, Turning | Santa Clara, CA | MillingTurning | - |
| Locdown Com Laser, Bending, Welding, Finishing | Brea, CA | LaserBendingWeldingFinishing | - |
| Long Machine Milling, Turning, Grinding | Temecula, CA | MillingTurningGrinding | - |
| LP Precision, Inc Milling, Turning, Grinding, Finishing | Santa Clara, CA | MillingTurningGrindingFinishing | - |
| LT CNC Machining Inc. Milling, Turning, Welding · AS9100 | San Diego, CA | MillingTurningWelding | AS9100 |
| Ltmt Machining LLC Milling, Finishing | Santa Clara, CA | MillingFinishing | - |
| Luna's Sheet Metal Inc Milling, Turning, Bending, Laser, Welding | Santa Clara, CA | MillingTurningBendingLaserWelding | - |
| M&M Machining, Inc Milling, Turning, Welding, Finishing | Ventura, CA | MillingTurningWeldingFinishing | - |
| Machina Labs Inc Stamping · ITAR, CMMC | Chatsworth, CA | Stamping | ITAR, CMMC |
| Machine Dimension, Inc Milling | San Jose, CA | Milling | - |
| Machinist Lab Milling, EDM | San Diego, CA | MillingEDM | - |
| Magna Tool Inc Milling, Turning, Welding · AS9100 | Cypress, CA | MillingTurningWelding | AS9100 |