| 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 |
| 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 | - |
| 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 |
| 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 |
| 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 |
| Orc Products Inc Milling, Turning · ISO 9001, AS9100 | Springdale, AR | MillingTurning | ISO 9001, AS9100 |
| Ozark Steel Llc Milling, Bending, Laser, Welding · ISO 9001 | Tulsa, OK | MillingBendingLaserWelding | ISO 9001 |
| Professional Machining Inc Milling, Turning | Oklahoma City, OK | MillingTurning | - |
| Slag Factory Milling, Laser, Welding | Oroville, CA | MillingLaserWelding | - |
| Southwest Greene International Inc Milling, Turning, Stamping, Metal AM, EDM | Oceanside, CA | MillingTurningStampingMetal AMEDM | - |
| Summit Machine Tool LLC Milling, Turning | Oklahoma City, OK | MillingTurning | - |
| Swissturn/usa, Inc Milling, Turning, Swiss, Grinding, Finishing · ISO 9001, ITAR, CMMC | Oxford, MA | MillingTurningSwissGrindingFinishing | ISO 9001, ITAR, CMMC |
| Takfab Precision Gunsmithing LLC Milling, Welding | Oak Harbor, WA | MillingWelding | - |
| The Toolroom, Inc Milling, Punching, Welding, EDM | Owensville, MO | MillingPunchingWeldingEDM | - |
| Toolco Inc Milling, Turning, Welding, Stamping, EDM, Grinding | Owensboro, KY | MillingTurningWeldingStampingEDMGrinding | - |
| Torq Manufacturing Milling, Turning, Assembly | Ogden, UT | MillingTurningAssembly | - |
| United Machining Service Inc Milling, Turning, Welding, Stamping, Finishing, Assembly · ISO 9001 | Orlando, FL | MillingTurningWeldingStampingFinishingAssembly | ISO 9001 |
| Vangor Engineering Corporation, the Milling, Swiss, Casting · AS9100 | Oxford, CT | MillingSwissCasting | AS9100 |
| 110 Metalworks Inc Milling, Turning, Laser, Bending, Welding, Finishing · ISO 9001, AS9100, ITAR | Liverpool, NY | MillingTurningLaserBendingWeldingFinishing | ISO 9001, AS9100, ITAR |
| 4-M Precision Industries Inc Milling, Turning, Laser, Bending, Welding, Stamping, Finishing · ISO 9001 | Auburn, NY | MillingTurningLaserBendingWeldingStampingFinishing | ISO 9001 |
| A.m.i. Engineering Co LLC Milling, Turning, Finishing · ISO 9001, ITAR | Santa Ana, CA | MillingTurningFinishing | ISO 9001, ITAR |
| AAT Omega, LLC Milling, Turning, Laser, Punching, Bending, Welding, EDM, Grinding, Finishing, Assembly · ISO 9001, AS9100, ITAR, NADCAP | Keystone Heights, FL | MillingTurningLaserPunchingBendingWeldingEDMGrindingFinishingAssembly | ISO 9001, AS9100, ITAR, NADCAP |
| Able Craft Fabrications, Inc Milling, Turning, Finishing, Assembly · ISO 9001 | Hopkins, MN | MillingTurningFinishingAssembly | ISO 9001 |
| Abston Machine Shop Inc Milling, Turning, Finishing · ISO 9001, ITAR | Taft, TN | MillingTurningFinishing | ISO 9001, ITAR |
| Advanced CNC Manufacturing Inc Milling, Grinding · ISO 9001 | Odessa, FL | MillingGrinding | ISO 9001 |
| Advanced Machining & Tooling, LLC Milling, Turning, Welding, Stamping, EDM, Grinding, Finishing · ISO 9001 | Salisbury, NC | MillingTurningWeldingStampingEDMGrindingFinishing | ISO 9001 |
| Aero Tech Manufactuting Inc Milling, Turning, Laser, Punching, Bending, Welding, Finishing, Assembly · ISO 9001 | North Salt Lake, UT | MillingTurningLaserPunchingBendingWeldingFinishingAssembly | ISO 9001 |
| Aeroparts Fabricating & Machining Inc Milling, Punching, Bending, Finishing · ISO 9001, AS9100, NADCAP | Nicktown, PA | MillingPunchingBendingFinishing | ISO 9001, AS9100, NADCAP |
| ALC Engineered Solutions Company Milling, Turning, Swiss, EDM, Finishing · ISO 9001 | Lockwood, MO | MillingTurningSwissEDMFinishing | ISO 9001 |
| All Materials Manufacturing Co LLC Milling, Turning, Swiss, Finishing · ISO 9001, AS9100, ITAR | Riverside, CA | MillingTurningSwissFinishing | ISO 9001, AS9100, ITAR |
| Alpha Omega Machining Inc Milling, Turning, Welding, EDM, Finishing · ISO 9001 | Painesville, OH | MillingTurningWeldingEDMFinishing | ISO 9001 |
| Alziebler Incorporated Milling, Turning, Welding, Grinding, Finishing · ISO 9001, AS9100, ITAR, NADCAP | Arleta, CA | MillingTurningWeldingGrindingFinishing | ISO 9001, AS9100, ITAR, NADCAP |
| American Hollow Boring Co Milling, Turning, Grinding, Finishing · ISO 9001 | Erie, PA | MillingTurningGrindingFinishing | ISO 9001 |
| Amincor Milling, Turning, Swiss, Laser, Punching, Bending, Welding, Stamping, EDM, Grinding, Finishing, Assembly · ISO 9001, ITAR, CMMC | Belton, MO | MillingTurningSwissLaserPunchingBendingWeldingStampingEDMGrindingFinishingAssembly | ISO 9001, ITAR, CMMC |