| Omni Precision Components Milling, Turning, Finishing · ISO 9001 | Holland, MI | MillingTurningFinishing | ISO 9001 |
| One Source Manufacturing Technology LLC Milling, Turning, Welding, Grinding, Finishing · ISO 9001, AS9100 | Leander, TX | MillingTurningWeldingGrindingFinishing | ISO 9001, AS9100 |
| Opti-Forms Inc Stamping, EDM, Finishing · ISO 9001, ITAR | Temecula, CA | StampingEDMFinishing | ISO 9001, ITAR |
| Orion Precision Industries, Inc Swiss, Bending, Finishing · ISO 9001, ITAR | Somerset, NJ | SwissBendingFinishing | ISO 9001, ITAR |
| Ortiz Tool, LLC Milling, Turning, Finishing, Assembly · ISO 9001, AS9100, ITAR, NADCAP | Windsor, CT | MillingTurningFinishingAssembly | ISO 9001, AS9100, ITAR, NADCAP |
| Pierce Steel Fabricators & Machining, Inc Punching, Bending, Welding, Finishing | Olean, NY | PunchingBendingWeldingFinishing | - |
| Precisioncore Manufacturing LLC Milling, Laser, Bending, Finishing · CMMC | Orange City, FL | MillingLaserBendingFinishing | CMMC |
| Square One Coating Systems LLC Finishing · NADCAP | Oriskany, NY | Finishing | NADCAP |
| Acc Precision Inc Milling, Turning, Welding, Grinding | Oxnard, CA | MillingTurningWeldingGrinding | - |
| Advanced Ceramic Technology Grinding · ITAR | Orange, CA | Grinding | ITAR |
| Advanced Machining Solutions Milling, Turning, Welding | Oklahoma City, OK | MillingTurningWelding | - |
| Albert Precision Machining Milling, Turning, Grinding | Omaha, NE | MillingTurningGrinding | - |
| American Machining Inc Milling, Turning, Welding, Grinding, Finishing · ISO 9001 | Ottawa, IL | MillingTurningWeldingGrindingFinishing | ISO 9001 |
| Apex Precision CNC Milling, Turning, Punching, Bending, Stamping, Casting, EDM, Grinding, Assembly · ITAR, CMMC | Orem, UT | MillingTurningPunchingBendingStampingCastingEDMGrindingAssembly | ITAR, CMMC |
| Benson Machine Works Inc. Turning, Bending, Laser, Welding | Omaha, NE | TurningBendingLaserWelding | - |
| BMW Precision Machining Milling, Turning, Swiss · ITAR | Oceanside, CA | MillingTurningSwiss | ITAR |
| Casemer Tool & Machine Inc Milling, Turning, Laser, Waterjet, Welding, EDM, Grinding | Oxford, MI | MillingTurningLaserWaterjetWeldingEDMGrinding | - |
| CNC Innotech LLC Milling, Turning, Swiss | Ogdensburg, NJ | MillingTurningSwiss | - |
| Council Stainless & Sheet Metal Bending, Welding, Waterjet | Oklahoma City, OK | BendingWeldingWaterjet | - |
| Custom Welding by Law, Inc Waterjet, Bending, Welding | Orlando, FL | WaterjetBendingWelding | - |
| D & H Industries Inc Milling, Turning, Laser, Bending, Welding, Stamping, Grinding, Finishing · ISO 9001, ITAR | Oconomowoc, WI | MillingTurningLaserBendingWeldingStampingGrindingFinishing | ISO 9001, ITAR |
| Davis Machine Works of Opelika Inc Welding | Opelika, AL | Welding | - |
| Elemetal Fabrication and Machine (Formerly American Machine Works) Milling, Bending, Welding, Waterjet | Omaha, NE | MillingBendingWeldingWaterjet | - |
| Foremaster Tool Company Milling, Turning, Welding, EDM, Grinding, Assembly | Ogden, UT | MillingTurningWeldingEDMGrindingAssembly | - |
| Fundom Enterprises Inc Milling, Turning, EDM, Grinding | Oklahoma City, OK | MillingTurningEDMGrinding | - |
| Hartman Enterprises Milling, Turning, Swiss, Grinding, Finishing · ISO 9001, AS9100, ITAR | Oneida, NY | MillingTurningSwissGrindingFinishing | ISO 9001, AS9100, ITAR |
| Hennemuth Metal Fabricators Bending, Welding, Waterjet | Oakdale, PA | BendingWeldingWaterjet | - |
| Laserworx Mfg Laser, Bending, Welding, Stamping · AS9100, ITAR | Oxnard, CA | LaserBendingWeldingStamping | AS9100, ITAR |
| Legion Metals Welding | Oklahoma City, OK | Welding | - |
| M & R Engineering Milling, Turning, Swiss, Finishing, Assembly · ISO 9001, AS9100, ITAR, NADCAP | Orange, CA | MillingTurningSwissFinishingAssembly | ISO 9001, AS9100, ITAR, NADCAP |
| Meyer Tool & Manufacturing, Inc Milling, Turning, Welding · ITAR | Oak Lawn, IL | MillingTurningWelding | ITAR |
| National Technologies, Inc Milling, Turning, Swiss, Grinding | Oak Creek, WI | MillingTurningSwissGrinding | - |
| Nuclear Lead Co, Inc Welding, Casting | Oak Ridge, TN | WeldingCasting | - |
| O & F Machine Products Co Milling, Turning, Swiss, EDM, Grinding · ISO 9001, AS9100, ITAR, NADCAP | Joplin, MO | MillingTurningSwissEDMGrinding | ISO 9001, AS9100, ITAR, NADCAP |
| O&R Precision Milling, Turning, Swiss, Stamping, EDM, Grinding · ISO 9001 | Berne, IN | MillingTurningSwissStampingEDMGrinding | ISO 9001 |
| Oakes Manufacturing LLC Milling, Turning, Assembly · ISO 9001 | Fort Collins, CO | MillingTurningAssembly | ISO 9001 |
| Octal Corporation Milling, Turning, Welding, Grinding, Assembly · ISO 9001, AS9100 | Teaneck, NJ | MillingTurningWeldingGrindingAssembly | ISO 9001, AS9100 |
| Oem Fabricators Inc Milling, Turning, Laser, Welding, Assembly · ISO 9001 | Woodville, WI | MillingTurningLaserWeldingAssembly | ISO 9001 |
| OGS Industries Turning, Bending, Laser, Welding, Stamping · ISO 9001, AS9100, ITAR, IATF 16949 | Akron, OH | TurningBendingLaserWeldingStamping | ISO 9001, AS9100, ITAR, IATF 16949 |
| Oil City Iron Works, Inc Milling, Casting · ISO 9001 | Corsicana, TX | MillingCasting | ISO 9001 |
| Olson Custom Designs LLC Milling, Turning, Bending, Welding · ISO 9001, ITAR, ISO 13485 | Indianapolis, IN | MillingTurningBendingWelding | ISO 9001, ITAR, ISO 13485 |
| Omega One Research, Inc Milling · ISO 9001, AS9100, ITAR | Boca Raton, FL | Milling | ISO 9001, AS9100, ITAR |
| Omega Precision Milling, Turning · ISO 9001 | Santa Fe Springs, CA | MillingTurning | ISO 9001 |
| Omega Tool & Machine Casting · ISO 9001 | Battle Creek, MI | Casting | ISO 9001 |
| Omikron Engineering, Inc Milling, Turning, Swiss, Assembly · ISO 9001 | Chatsworth, CA | MillingTurningSwissAssembly | ISO 9001 |
| Omw Corp Milling, Assembly · ISO 9001, AS9100, CMMC | Novato, CA | MillingAssembly | ISO 9001, AS9100, CMMC |
| Onamac Industries, Inc Milling, Turning, Casting, Grinding · ISO 9001, AS9100 | Everett, WA | MillingTurningCastingGrinding | ISO 9001, AS9100 |
| Onium Machine and Fabrication, LLC Milling, Turning, Laser, Bending, Welding, Assembly · ISO 9001 | Winder, GA | MillingTurningLaserBendingWeldingAssembly | ISO 9001 |
| Onodi Tool & Engineering Co Milling, Turning, Welding, Assembly · ISO 9001 | Melvindale, MI | MillingTurningWeldingAssembly | ISO 9001 |
| Optima Precision Milling, Turning, Bending, Welding, EDM, Metal AM · ISO 9001, AS9100, ISO 13485, NADCAP | San Jose, CA | MillingTurningBendingWeldingEDMMetal AM | ISO 9001, AS9100, ISO 13485, NADCAP |