| Mimic Manufacturing, LLC Welding, Finishing | Heavener, OK | WeldingFinishing | - |
| Mirror Finish Polishing Welding, Casting, Grinding | Kearney, MO | WeldingCastingGrinding | - |
| MM Industries Tech LLC Laser, Punching, Bending, Welding, Assembly | Stanwood, WA | LaserPunchingBendingWeldingAssembly | - |
| Models & Tools Inc Milling, Turning, Welding · AS9100 | Shelby Township, MI | MillingTurningWelding | AS9100 |
| Modern Machine Works Milling, Turning, Welding, EDM, Grinding, Finishing | Albany, OR | MillingTurningWeldingEDMGrindingFinishing | - |
| Mofab Inc Milling, Laser, Waterjet, Bending, Welding | Anderson, IN | MillingLaserWaterjetBendingWelding | - |
| Moll Machine Works, LLC Milling, Turning, Welding | Williamson, NY | MillingTurningWelding | - |
| Monarch Valve Corp Milling, Turning, Welding, Grinding, Assembly · ISO 9001 | Aston, PA | MillingTurningWeldingGrindingAssembly | ISO 9001 |
| Mono Engineering Corp Turning, Welding, EDM · ISO 9001 | Chatsworth, CA | TurningWeldingEDM | ISO 9001 |
| Montgomery Dynamics Milling, Turning, Welding · ISO 9001, ITAR | Huntingdon Valley, PA | MillingTurningWelding | ISO 9001, ITAR |
| Morehead Machinery Inc Milling, Turning, Welding, EDM, Grinding | Elkhart, IN | MillingTurningWeldingEDMGrinding | - |
| Morena Welding Inc Welding | San Diego, CA | Welding | - |
| Morgan Bronze Products, Inc Turning, Welding, Casting · ISO 9001 | Lake Zurich, IL | TurningWeldingCasting | ISO 9001 |
| Morrison Industries LLC Milling, Turning, Laser, Bending, Welding, Finishing, Assembly | Morrison, TN | MillingTurningLaserBendingWeldingFinishingAssembly | - |
| Motion Metalworks LLC Laser, Waterjet, Bending, Welding, Finishing | Wrens, GA | LaserWaterjetBendingWeldingFinishing | - |
| Mountain CNC Milling, Turning, Waterjet, Welding, Grinding, Finishing, Assembly · ITAR, CMMC | Loveland, CO | MillingTurningWaterjetWeldingGrindingFinishingAssembly | ITAR, CMMC |
| Mountain Machine Works Milling, Turning, Welding · ISO 9001, ITAR | Auburn, ME | MillingTurningWelding | ISO 9001, ITAR |
| Mountain Manufacturing, LLC Milling, Laser, Bending, Welding, Finishing, Assembly · ISO 13485 | Post Falls, ID | MillingLaserBendingWeldingFinishingAssembly | ISO 13485 |
| Mountain Precision Tool Co, Inc Milling, Turning, Laser, Waterjet, Punching, Bending, Welding, EDM, Grinding, Finishing | Blacksburg, VA | MillingTurningLaserWaterjetPunchingBendingWeldingEDMGrindingFinishing | - |
| Mountain Valley Machine, Inc Milling, Turning, Waterjet, Bending, Welding, EDM, Grinding · ISO 9001 | Smithfield, UT | MillingTurningWaterjetBendingWeldingEDMGrinding | ISO 9001 |
| Mountain View Machine and Welding Milling, Turning, Waterjet, Welding, EDM | Logan, UT | MillingTurningWaterjetWeldingEDM | - |
| MRC Machine Inc Milling, Turning, Welding | Pound, WI | MillingTurningWelding | - |
| MSP Maufacturing Milling, Turning, Bending, Welding, Finishing, Assembly | Bloomington, IN | MillingTurningBendingWeldingFinishingAssembly | - |
| NKP Metals LLC Waterjet, Welding | Chicago, IL | WaterjetWelding | - |
| O & Y Precision Inc Milling, Laser, Waterjet, Bending, Welding, EDM, Finishing, Assembly | Morgan Hill, CA | MillingLaserWaterjetBendingWeldingEDMFinishingAssembly | - |
| O. W. Landergren, Inc Milling, Laser, Punching, Bending, Welding, Stamping, EDM, Grinding, Finishing | Pittsfield, MA | MillingLaserPunchingBendingWeldingStampingEDMGrindingFinishing | - |
| O'Connell Machinery Co Inc Milling, Welding | Buffalo, NY | MillingWelding | - |
| Octal Corporation Milling, Turning, Welding, Grinding, Assembly · ISO 9001, AS9100 | Teaneck, NJ | MillingTurningWeldingGrindingAssembly | ISO 9001, AS9100 |
| Odat Machine Milling, Turning, Welding, Grinding | Gorham, ME | MillingTurningWeldingGrinding | - |
| Odin Fabrication, Inc Laser, Punching, Welding, Finishing | Elburn, IL | LaserPunchingWeldingFinishing | - |
| OGS Industries Turning, Bending, Laser, Welding, Stamping · ISO 9001, AS9100, ITAR, IATF 16949 | Akron, OH | TurningBendingLaserWeldingStamping | ISO 9001, AS9100, ITAR, IATF 16949 |
| Olson & Co. Steel Welding | Fresno, CA | Welding | - |
| Olson Custom Designs LLC Milling, Turning, Bending, Welding · ISO 9001, ITAR, ISO 13485 | Indianapolis, IN | MillingTurningBendingWelding | ISO 9001, ITAR, ISO 13485 |
| Olympic Industries Laser, Welding, Stamping | Cordova, TN | LaserWeldingStamping | - |
| Omni Machine Works Inc Milling, Turning, Welding, EDM, Grinding | Covington, GA | MillingTurningWeldingEDMGrinding | - |
| 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 |
| Operateup Inc Milling, Turning, Punching, Welding, Stamping · ISO 9001 | Orange, MA | MillingTurningPunchingWeldingStamping | ISO 9001 |
| Orange County Sheet Metal Shop Bending, Laser, Welding, Stamping | Anaheim, CA | BendingLaserWeldingStamping | - |
| Orlando Metal Fabrication Inc Milling, Waterjet, Punching, Bending, Welding, Finishing · ISO 9001, AS9100 | Orlando, FL | MillingWaterjetPunchingBendingWeldingFinishing | ISO 9001, AS9100 |
| Oscar's Custom Iron Works Welding | San Antonio, TX | Welding | - |
| Ottenweller Company, Inc. Bending, Laser, Welding · ISO 9001 | Fort Wayne, IN | BendingLaserWelding | ISO 9001 |
| Owens Industries, Inc. Milling, Turning, Welding, EDM, Casting, Metal AM · ISO 9001, AS9100 | Oak Creek, WI | MillingTurningWeldingEDMCastingMetal AM | ISO 9001, AS9100 |
| P & N Machine Co, Inc Milling, Turning, Swiss, Laser, Welding, EDM, Finishing · ISO 9001, ITAR, ISO 13485 | Houston, TX | MillingTurningSwissLaserWeldingEDMFinishing | ISO 9001, ITAR, ISO 13485 |
| P&M Steel Company Welding | Sioux Falls, SD | Welding | - |
| P3D Creations LLC Milling, Turning, Welding, EDM, Grinding, Finishing · ITAR, CMMC | Maitland, FL | MillingTurningWeldingEDMGrindingFinishing | ITAR, CMMC |
| Pacon Mfg, Inc Milling, Turning, Welding, Finishing · ISO 9001 | Livermore, CA | MillingTurningWeldingFinishing | ISO 9001 |
| Painter Tool Incorporated Milling, Turning, Welding, EDM | Irwin, PA | MillingTurningWeldingEDM | - |
| Paligen Technologies Welding, Forging | Garland, TX | WeldingForging | - |
| Palmetto Precision Machining, Inc Milling, Welding, EDM, Grinding · ISO 9001 | Anderson, SC | MillingWeldingEDMGrinding | ISO 9001 |