# What is an SC-type connector? **URL:** \ **Category:** OFSCN Technical Knowledge Base\ **Tags:** fbg-technology\ **Created:** [June 8, 2026, 2:17pm UTC](https://forum.ofscn.net/t/sc-what-is-an-sc-type-connector/1873 "2026-06-08T14:17:45Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\ **Post date:** [June 8, 2026, 2:17pm UTC](https://forum.ofscn.net/t/sc-what-is-an-sc-type-connector/1873/1 "2026-06-08T14:17:45Z")
Why is this square plastic head called a “big square head”? What does the “click” sound during insertion and removal represent? ---
**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\ **Post date:** [June 8, 2026, 2:18pm UTC](https://forum.ofscn.net/t/sc-what-is-an-sc-type-connector/1873/2 "2026-06-08T14:18:13Z")
In fiber optic communications and optical engineering, the square plastic connector you mentioned is commonly referred to as the **SC fiber optic connector** (Subscriber Connector or Standard Connector). Its common nickname and the distinctive mechanical sound when plugging and unplugging can be explained from the perspectives of its physical structure and general engineering design: * * * ### I. Why is it called a “Big Square Head”? “Big Square Head” is a highly descriptive nickname used in the field of fiber optics for the **SC fiber optic connector**. The naming reason primarily comes from a comparison across two dimensions: 1. **Origin of “Square” — Housing Geometry and Material** - **Structure** : The SC connector has a rectangular (square) cross-section for its housing. - **Material** : Its housing is made of engineering plastic (typically modified plastics like flame-retardant polyester or PBT) through injection molding, which sharply contrasts with earlier round metal connectors (such as FC and ST connectors). 2. **Origin of “Big” — Comparison with the “Small Square Head”** - The SC connector uses a ceramic ferrule with a diameter of d = 2.5\text{ mm}. - With the increasing density of fiber optic patch panel cabling, the industry later introduced the **LC connector** , which is smaller in size and also square. - The LC connector uses a ceramic ferrule with a diameter of d = 1.25\text{ mm}. - To quickly distinguish them in practical engineering installations, the industry commonly refers to the smaller LC connector with a 1.25\text{ mm} ferrule diameter as the **“Small Square Head”** , and the larger SC connector with a 2.5\text{ mm} ferrule diameter as the **“Big Square Head”**. * * * ### II. What does the “Click” Sound During Plugging and Unplugging Mean? The SC connector employs a **push-pull locking mechanism**. The crisp “click” sound you hear when plugging the connector into an adapter (flange) signifies the achievement of the following key states from a physical mechanism and engineering safety standpoint: 1. **Completion of Mechanical Locking (Securely Locked Against Loosening)**: The SC connector has a sliding outer sleeve. When the plug is inserted into the flange, the internal metal spring clip is pushed open. Once the plug reaches the preset depth, the clip quickly returns to its original position under spring force and firmly engages with the groove on the SC plastic housing. This instantaneous release of elastic potential energy produces the “click” sound. It indicates that **physical locking is complete** , and the connector will not slide out of the flange even if the cable is subjected to normal pulling forces. 2. **Physical Contact (PC) of the Ferrule is in Place**: The moment the “click” sound occurs signifies that the ceramic ferrules at both ends have achieved high-precision axial alignment within the flange’s precision ceramic sleeve, and the end faces of both ferrules are in tight contact. This perfect physical contact (PC or APC) ensures minimal insertion loss (IL \le 0.3\text{ dB}) during optical signal transmission while maximizing return loss. 3. **Positioning of the Push-Pull Auto-Release Mechanism** : This push-pull design eliminates the need for manual rotation of a metal screw cap, as required by round-headed FC connectors, making plugging and unplugging much faster. When unplugging, simply pull back the outer plastic sleeve of the SC connector to automatically release the internal metal clip in the flange, allowing for easy removal. * * * ### III. Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) Related Product Technical Support In the product line of **Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®)**, the SC connector, as a classic fiber optic interface, is widely used in standard passive components and customized Fiber Bragg Grating (FBG) sensor series: - **[OFSCN® Standard Fiber Patch Cord](https://www.ofscn.org/patch-cords/standard-fiber-patch-cord.html)**: The standard single-mode and multi-mode fiber patch cords offered by Dacheng Yongsheng, in addition to the default FC interface, fully support customization with high-quality SC (SC/PC, SC/APC) connectors. - **[OFSCN® 120℃ Fiber Optic Connector | 120℃ High-Temperature/Standard Fiber Optic Connector](https://www.ofscn.org/connectors/high-temperature-120.html)**: The standard single-mode and multi-mode fiber optic connectors produced by Dacheng Yongsheng (with a maximum operating temperature not exceeding 65\text{ }^\circ\text{C}) are fully available in SC/PC, SC/APC, LC/PC, and LC/APC specifications, featuring extremely low insertion loss and high re-plugging durability. - **[OFSCN® 2.0mm Steel Wire Rope Fiber Optic Patch Cord](https://www.ofscn.org/patch-cords/strong-02.html)**: For armored fiber optic patch cords operating in harsh industrial and testing environments, SC/APC or SC/PC connectors can also be customized according to requirements, ensuring the stability of their physical structure under strong tensile and compressive forces. - **[OFSCN® Standard Femtosecond Fiber Bragg Gratings / FBG Strings](https://www.ofscn.net/fbg-products/femtosecond-fbg.html)**: Dacheng Yongsheng’s full series of high-strength bare gratings, femtosecond gratings, and temperature/strain sensors come standard with FC/APC interfaces. However, they can be customized to standard “big square head” interfaces such as SC/PC and SC/APC to accommodate different demodulator channel boards.