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.
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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 | Contact system | Status / role |
|---|---|---|---|
| Standard-A | USB-A | 4 contacts | Original host/downstream form; legacy but still widespread |
| SuperSpeed Standard-A | USB-A | 9 contacts | USB 3.x host/downstream form with added SuperSpeed contacts |
| Standard-B | USB-B | 4 contacts | Original peripheral/upstream form |
| SuperSpeed Standard-B | USB-B | 9 contacts | USB 3.x peripheral form with an enlarged upper section |
| Powered-B | USB-B | 11 contacts | Rare USB 3.x B variant with two added adapter-power contacts |
| Mini-A | Mini-USB | 5 contacts | Historical OTG host form; antiquated and prohibited for new USB-IF certification |
| Mini-B | Mini-USB | 5 contacts | Legacy device/peripheral form; use remains permitted, but new connector certification ended in 2021 |
| Mini-AB | Mini-USB | 5-contact receptacle | Historical OTG dual-role receptacle; antiquated and prohibited for new USB-IF certification |
| Micro-A | Micro-USB | 5-contact plug | Legacy OTG host-side form; USB-IF ended OTG product certification in 2019 |
| Micro-B | Micro-USB | 5 contacts | Widely used legacy compact device/peripheral form |
| Micro-AB | Micro-USB | 5-contact receptacle | Legacy OTG dual-role receptacle; USB-IF ended OTG product certification in 2019 |
| SuperSpeed Micro-A | SuperSpeed Micro | 10-contact plug | Rare USB 3.x OTG host-side form; USB-IF ended OTG product certification in 2019 |
| SuperSpeed Micro-B | SuperSpeed Micro | 10 contacts | Legacy USB 3.x peripheral form; new connector certification ended after February 28, 2021 |
| SuperSpeed Micro-AB | SuperSpeed Micro | 10-contact receptacle | Rare USB 3.x OTG dual-role receptacle; new connector certification ended after February 28, 2021 |
| Full-Featured Type-C | USB Type-C | Full high-speed Type-C contact system | Current implementation for USB 3.2, USB4, USB 2.0, power, and supported sideband functions |
| USB 2.0 Type-C | USB Type-C | Reduced Type-C contact system | Current reduced implementation for USB 2.0 data and Type-C power |
| Power-Only Type-C | USB Type-C | Reduced power/configuration contacts | Current implementation for Type-C power without USB data |
| Single-Screw Locking Type-C | USB Type-C | Type-C plug plus one locking screw | Standardized secured-cable mechanical form |
| Dual-Screw Locking Type-C | USB Type-C | Type-C plug plus two locking screws | Standardized secured-cable 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 nine additional interfaces are materially distinct USB-related mating forms documented by USB-IF or in published PC implementation specifications. They are separated from the external connector table because several are reference designs or platform interfaces rather than USB base-spec cable connectors.
| 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.
