SC, FC and ST all use a 2.5 mm ferrule, so their optical performance is the same for the same polish and grade. SC pushes and clicks, FC screws on with a threaded nut, and ST twists with a bayonet. Choose SC for telecom panels, FC for instruments and vibration, ST for legacy multimode, and LC for new builds.
Pick one in a minute
Start from the equipment and the environment, because all three connectors carry the same 2.5 mm ferrule and the same optical performance when they are the same polish and grade. What differs is the housing: how it locks, how it resists movement, and where it is still installed.
| If you have | Choose | Why |
|---|---|---|
| Telecom equipment, passive optical networks, older patch panels | SC | Square push-pull body, quick to mate, widely installed in carrier gear |
| Test instruments, lab benches, lasers, equipment that is moved or vibrates | FC | Threaded nut holds the ferrule still, key keeps the rotation fixed |
| Older multimode building cabling, legacy military or industrial links | ST | Bayonet twist lock, springs hold the ferrule against its mate |
| A new build with no legacy kit | Probably none of the three | LC has overtaken them for density and is covered in the LC vs SC connector guide |
That table gets most buyers to the answer. The rest of this page explains the differences, so you can handle the awkward cases: mixed equipment, hybrid cords, vibration, and cleaning.
What the three connectors have in common
SC, FC and ST are all 2.5 mm ferrule connectors. The ferrule is a ceramic cylinder (usually zirconia) with the fibre bonded along its centre, and the two ferrules meet end to end inside a split sleeve. That is why a hybrid cord, say SC on one end and ST on the other, mates with each equipment port as if it had the same connector at both ends. The ferrule diameter is the same, so the optical interface is the same. Only the housing changes.
- Ferrule diameter: 2.5 mm for all three. LC and MU use 1.25 mm.
- Polish: PC, UPC or APC is available on all three, though FC and SC are more often found in APC form and ST is usually flat or UPC.
- Fibre: single-mode (OS1, OS2) and multimode (OM1 to OM4). The fibre grade is a cable choice and does not depend on the connector.
- Standards: IEC 61754 defines the connector interfaces (part 2 for ST, part 4 for SC, part 13 for FC). TIA's fibre optic connector intermateability standards (the FOCIS series) describe the same families.
Because the ferrule does the optical work, insertion loss and return loss depend on the polish, the ferrule quality and cleanliness, and not on the housing. A good SC and a good ST will match each other in loss. A poor one of either will not.
Locking and handling compared
| Feature | SC | FC | ST |
|---|---|---|---|
| How it locks | Push in, pull out. A latch inside the body holds it. | Threaded coupling nut screws onto the adapter | Push in and twist a quarter turn, bayonet lock |
| Key | Square body keys it by shape | A key on the ferrule housing fits a slot in the adapter | A key on the barrel fits a slot |
| Duplex use | Easy, two bodies clip into a duplex clip | Single connector per cord, no standard duplex clip | Single connector per cord |
| Vibration resistance | Moderate. The latch can loosen if pulled sideways. | Best of the three, since the thread holds the connector | Moderate to good. The spring and bayonet keep contact. |
| Speed of mating | Fastest | Slowest, thread must be turned | Fast, with a twist |
| Panel density | Higher than FC or ST | Lowest, round with a nut | Low, round with a barrel |
| Tool-free use with gloves | Yes | Possible, a little fiddly | Yes |
| Typical home | Telecom, FTTH, enterprise panels | Instruments, lasers, labs, some telecom | Legacy multimode LAN, some military and industrial links |
The practical difference shows up in the field. SC is mated by feel, in a crowded panel, and gives a click. FC takes time but stays put, which is why test equipment uses it, since a reference cord on a bench is plugged in hundreds of times and cannot drift. ST can twist the ferrule against its mate if the technician rotates the cable while tightening, and that is a source of intermittent loss on cords that are repeatedly handled.
Where each one came from, and what that means today
ST was introduced in the 1980s for multimode building and campus cabling and became the standard multimode connector for a generation of enterprise cabling. SC came from Japan and spread through telecom and early Fibre Channel and Ethernet gear, and it became a recommended connector in the structured cabling standards (TIA-568-A). FC, also of Japanese origin, was the first widely used ceramic ferrule connector in telecom and then moved to test equipment and lasers.
The result is a simple map. Buildings built in the late 1980s and 1990s with multimode cabling often have ST panels. Telecom exchanges, passive optical networks and many enterprise cabinets from the 1990s and 2000s have SC. Instruments and lab equipment still use FC because replacing the front panel is not worth the effort. New enterprise and data centre build-outs use LC. Mixed sites need hybrid cords.
If you are buying for an existing site, count the ports first. The age of the equipment is a better guide than the age of the connector design. Our broader fibre connector types guide shows where these three sit among LC, MTP and others, and the single pages on SC, ST and FC go into each one.
Worked example 1: a lab bench with mixed ports
This uses assumed values. A test lab has these instrument and device ports on a single-mode OS2 bench:
| Equipment | Port | Count |
|---|---|---|
| Laser source | FC/APC | 2 |
| Optical power meter | FC/UPC (with adapter) | 2 |
| OTDR | SC/APC | 1 |
| Legacy ST patch panel (multimode devices) | ST | 6 |
| Device under test | SC/APC | 4 |
The question is how many cord types the bench needs. Work through it by pair of ports:
- Laser (FC/APC) to device (SC/APC): FC/APC to SC/APC cord. Both ends are angled, so polish matches.
- Power meter (FC/UPC) to device (SC/APC): each end of the cord must match the port it meets, so the cord is FC/UPC at the meter and SC/APC at the device. A cord with different polish at its two ends is normal. What must never happen is APC meeting UPC at the same mating. See the APC to UPC mating mistakes guide.
- OTDR (SC/APC) to device (SC/APC): SC/APC to SC/APC cord, usually with a launch cable for events at the start.
- ST panel: the panel serves multimode devices, so it is a different fibre type altogether, and OS2 cords must not be used there.
The lab ends up with three cord types for single-mode, FC/APC to SC/APC, SC/APC to SC/APC, and FC/UPC to SC/APC, plus a separate multimode ST set. Writing it out takes ten minutes, and it prevents an order of the wrong cords arriving. The same logic applies to any site with mixed equipment, and for polish choices see connector polish types.
Worked example 2: loss in a mixed-connector link
Take a single-mode 1310 nm link with assumed values: 2 km of fibre at 0.35 dB/km, and four mated pairs along the path (patch panel at each end, with two cords). Compare two choices.
| Item | All-SC plant | SC panel, FC test cords |
|---|---|---|
| Fibre loss | 2 km × 0.35 = 0.70 dB | 0.70 dB |
| Mated pairs | 4 × 0.3 dB = 1.20 dB | 4 × 0.3 dB = 1.20 dB |
| Hybrid adapter at the test set | 0 | 1 × 0.3 dB = 0.30 dB |
| Total | 1.90 dB | 2.20 dB |
The extra 0.3 dB is one more mated pair at the test point, and it counts as loss only if the measurement setup includes it. This is why test procedures define a reference measurement with the same cords, so the adapter loss is removed from the reading. The calculation is the same one used in the fibre loss budget guide. The TIA structured cabling standard allows up to 0.75 dB per mated connector pair in the channel, but practical pairs land well below that, so use the data sheet value, and do not use the worst case for every pair.
Cleaning and inspection differences
The ferrule is the same, so end face care is the same. What differs is access. An SC in a crowded panel is cleaned with a push-in click cleaner, or a cassette cleaner for the adapter. An FC needs the nut unscrewed first, and the ferrule is easier to reach, but also easier to touch by mistake. An ST has a round barrel and can be wiped with a stick cleaner through the adapter. Inspect every connector before mating, to the end-face criteria of IEC 61300-3-35. Read the end-face cleaning and inspection guide before you buy a cleaning kit, since the right tool depends on the connector.
- Cap every connector when it is not mated. Reuse the caps that came with the cord.
- Do not clean a connector that is live. Switch the source off or disconnect it first.
- Do not touch the ferrule after cleaning. Handle the body.
Common mistakes
| Mistake | What goes wrong | Fix |
|---|---|---|
| Buying SC cords for an FC panel | They do not fit. The ferrule is the same and the housing is not. | Count the port type first, and write it on the order |
| Ordering APC for a UPC port | Return loss and insertion loss rise, and the end faces can be damaged | Match polish on both sides of every mating |
| Using multimode cords on single-mode links, or the reverse | High loss or a dead link. The connector type is irrelevant here. | Match the fibre type and core size at both ends |
| Over-tightening FC nuts with pliers | Cracked ferrules and bent keys | Finger tight only |
| Rotating an ST cord after it is engaged | The ferrules twist against each other and loss moves | Twist the connector body, not the cable |
| Buying cords for a new build in a legacy connector | Dense panels and new optics are LC-based | Use LC for new work and hybrids at the boundary |
| Choosing by price per cord only | The cheapest cord may use unmatched polish or poor ferrules | Ask for loss and return loss limits in the quote |
Buyer checklist
- List the ports at both ends and their connector type (SC, FC, ST, LC).
- Note the polish at each port: PC, UPC or APC. APC is marked green and UPC is blue or beige in the usual colour scheme, which is described in fibre colour codes.
- Decide the fibre: OS2 single-mode, or the multimode grade (OM1 to OM4) that matches the link.
- Choose simplex or duplex. SC duplex uses a clip. FC and ST are usually ordered as simplex pairs.
- Measure the length along the route and add slack.
- Choose the jacket: 2 mm or 3 mm, riser or LSZH, as in the 2 mm vs 3 mm patch cord cable guide.
- Write the full line: connector A, connector B, polish, fibre, length, jacket, quantity.
For single cords, a short line is fine. For a mix of types, put the lines in a table, and send it with the RFQ. The RFQ guide shows the full layout.
When none of the three is the right choice
If your equipment uses 1.25 mm LC interfaces, fit LC patch cords. If you need hundreds of fibres in a rack, use MPO. If the link lies outdoors in water or dust, a standard SC, FC or ST in an ordinary adapter is the wrong answer, and a sealed connector series does the job, as explained in our guide to IP67 and IP68 fibre connectors. If the link needs an extremely high return loss, check the data sheet for APC performance, since not every FC or ST variant is offered with an angled polish.
Request a quote
Radix Fibrotech makes fibre optic patch cords and assemblies to the customer's drawing in Pune, including SC, FC and ST ends and hybrids between them. Send the connector at each end, polish, fibre type, length, jacket and quantity through the request a quote page, or by phone or WhatsApp. For ready-made pages on cords see SC to SC patch cords and the wider fibre optic patch cords range.
Questions buyers ask
What is the difference between SC, FC and ST connectors?
All three use a 2.5 mm ferrule. SC is a push-pull square connector, FC locks with a threaded nut, and ST locks with a bayonet twist. The optical performance depends on polish and ferrule quality, not on the housing.
Can I connect an SC cable to an FC port?
Not directly, because the housings differ. Use a hybrid adapter or a hybrid patch cord with SC at one end and FC at the other. Match the polish (UPC or APC) at both ends of every mating.
Which is better, SC, FC or ST?
None is better in general. SC suits panels and telecom, FC suits instruments and vibration, ST suits legacy multimode. LC is now the usual choice for new enterprise and data centre work.
Are SC, FC and ST connectors single-mode or multimode?
They are available in both. The connector housing does not set the fibre type. The cord's fibre (OS2, OM1 to OM4) does, and it must match the fibre in the link.
Why is the FC connector used on test equipment?
The threaded nut holds the connector firmly and the key fixes its rotation, so the optical contact stays repeatable when the cord is mated many times and the equipment is moved or shaken.
Is ST connector obsolete?
It is a legacy connector, found in older multimode cabling and some military and industrial links. It is still used and still made, but new enterprise installations normally choose LC.
Do SC, FC and ST have the same insertion loss?
Typical insertion loss is similar for the same grade and polish, since the ferrule decides it. Check the loss and return loss limits in the data sheet or quote for the grade you order.
Can I mix APC and UPC connectors?
No. Mating an angled (APC) end with a flat (UPC) end gives high loss and can damage the end faces. Match the polish at each mating, or use a cord with APC at one end and UPC at the other only where each end meets its own type.