USB Reference
USB Connectors
USB physical interfaces range from familiar external Standard-A, Mini, Micro, and Type-C connectors to obscure embedded, motherboard, and front-panel interfaces.
Families · External Forms · Internal Interfaces · Articles
Related: USB Standards · USB Adapters · USB Charging
Standard external USB connector forms
These 19 forms cover the materially distinct external plug, receptacle, SuperSpeed, USB On-The-Go, reduced-function Type-C, and locking Type-C interfaces standardized in USB connector specifications.
| Connector form | Family | Contacts / form | Typical role | Status |
|---|---|---|---|---|
| Standard-A | USB-A | 4 contacts | Host / downstream | Legacy design; still widespread |
| SuperSpeed Standard-A | USB-A | 9 contacts | Host / downstream | USB 3.x form; still widely used |
| Standard-B | USB-B | 4 contacts | Peripheral / upstream | Legacy; still found on peripherals |
| SuperSpeed Standard-B | USB-B | 9 contacts | Peripheral / upstream | Legacy USB 3.x form |
| Powered-B | USB-B | 11 contacts | Peripheral plus adapter power | Rare USB 3.x variant |
| Mini-A | Mini-USB | 5 contacts | OTG host-side | Antiquated; prohibited for new USB-IF certification |
| Mini-B | Mini-USB | 5 contacts | Device / peripheral | Legacy; new connector certification ended in 2021 |
| Mini-AB | Mini-USB | 5-contact receptacle | OTG dual-role receptacle | Antiquated; prohibited for new USB-IF certification |
| Micro-A | Micro-USB | 5-contact plug | OTG host-side | Legacy; OTG product certification ended in 2019 |
| Micro-B | Micro-USB | 5 contacts | Device / peripheral | Legacy; still widespread on older devices |
| Micro-AB | Micro-USB | 5-contact receptacle | OTG dual-role receptacle | Legacy; OTG product certification ended in 2019 |
| SuperSpeed Micro-A | SuperSpeed Micro | 10-contact plug | USB 3.x OTG host-side | Rare legacy form |
| SuperSpeed Micro-B | SuperSpeed Micro | 10 contacts | USB 3.x device / peripheral | Legacy; new connector certification ended in 2021 |
| SuperSpeed Micro-AB | SuperSpeed Micro | 10-contact receptacle | USB 3.x OTG dual-role | Rare legacy form |
| Full-Featured Type-C | USB Type-C | Full high-speed Type-C contact system | Configurable data, power, and supported sideband roles | Current |
| USB 2.0 Type-C | USB Type-C | Reduced Type-C contact system | USB 2.0 data and Type-C power | Current reduced implementation |
| Power-Only Type-C | USB Type-C | Reduced power/configuration contacts | Type-C power without USB data | Current specialized implementation |
| Single-Screw Locking Type-C | USB Type-C | Type-C plug plus one locking screw | Secured Type-C cable connection | Current specialized mechanical form |
| Dual-Screw Locking Type-C | USB Type-C | Type-C plug plus two locking screws | Secured Type-C cable connection | Current specialized mechanical form |
Sources: USB-IF USB 2.0 Specification, USB-IF USB 3.2, USB-IF USB Type-C Cable and Connector Specification Release 2.5, USB-IF USB Type-C Locking Connector Specification, USB-IF OTG Compliance Updates, and USB-IF Cables and Connectors Compliance Updates.
Specialized and internal USB physical interfaces
These specialized USB interfaces cover embedded connectors, motherboard headers, and front-panel reference designs documented by USB-IF or published PC specifications.
| Physical interface | Published scope | Physical form | Typical use |
|---|---|---|---|
| USB Mezzanine Connector | USB-IF embedded-interface guideline | Specialized mezzanine mating interface | Compact embedded USB 2.0 peripheral connections |
| USB Thin Card | USB-IF cable and connector specification | Thin card-format physical interface | Rare removable or embedded card-format USB hardware |
| USB 2.0 Front-Panel Header | Published PC system-design interface | 2×5, 2.54 mm; keyed at pin 9 | Two front-panel USB 2.0 ports |
| USB 2.0 Dual Internal Header | Published PC system-design interface | 2×5, 2.54 mm; keyed at pins 9 and 10 | Two internal USB 2.0 devices |
| USB 2.0 Single Internal Header | Published PC system-design interface | 1×5, 2.54 mm; keyed at pin 5 | One internal USB 2.0 device |
| USB 3.0 Internal Header | Intel USB 3.0 internal connector specification | 2×10 keyed header with 19 active contacts | Two SuperSpeed USB front-panel ports |
| Key-A 20-Pin Front-Panel Connector | USB-IF desktop reference design | 20-pin Key-A header/plug | One Type-C or one Standard-A front-panel port |
| Key-B 20-Pin Front-Panel Connector | USB-IF desktop reference design | 20-pin Key-B header/plug | Two Standard-A front-panel ports |
| 40-Pin Front-Panel Connector | USB-IF desktop reference design | 40-pin header/plug | Two Type-C, mixed Type-C/Standard-A, or two Standard-A ports |
Sources: USB-IF USB Connector for Mezzanine Applications Guidelines, USB-IF USB Thin Card documents, Intel Thin Mini-ITX Based PC System Design Guide, Intel USB 3.0 Internal Connector and Cable Specification, and USB-IF Desktop Front Panel Cable and Connector Implementation Document.
USB connector articles
Explore practical guides on USB connector compatibility, damaged or loose ports, reversible plugs, and common connection problems across devices.
