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SFIC (small format interchangeable core) is the figure-eight core that is standardized across brands, so it is the default choice for new systems and mixed-brand buildings. LFIC (large format interchangeable core) is a larger, brand-specific core. Buy LFIC only when your existing locks are built for it, such as Sargent, Corbin Russwin or Schlage full-size (FSIC) hardware, and you want to keep that key system. The two formats never interchange.

SFIC vs LFIC: comparison table

Feature	SFIC (small format)	LFIC (large format)
Shape and size	Compact figure-eight profile	Larger body; size and shape vary by manufacturer
Pin diameter	0.108 in	0.115 in
Pin count	6 or 7 pins	6 pins is typical (Schlage FSIC is offered in 6-pin length)
Cross-brand fit	Standardized: an SFIC core fits an SFIC housing from another maker (Best, Schlage, Falcon and others)	Brand-specific: a Yale LFIC core will not fit a Schlage LFIC housing
Control key	Yes, removes the core without disassembling the lock	Yes, same principle
Best for	New installs, mixed brands, retrofits, rim cylinders on exit devices, construction cores	Facilities that already run one maker's LFIC locks and want to keep the key system

Pin sizes come from Locksmith Ledger; pin counts and compatibility come from the Schlage and dormakaba pages listed under Official sources.

What is an SFIC core?

An SFIC is a small-format removable core, shaped like a figure eight, that a control key releases from its housing without taking the lock apart. The format was originated by Best Access (now dormakaba) and is built by many makers, so a core from one brand fits another brand's SFIC housing. SFIC cores are made in 6-pin and 7-pin lengths. Locksmith Ledger puts North American commercial use at more than 100 million SFIC cores.

Because the format is standard, you can specify SFIC "regardless of existing hardware brands." Schlage also offers SFIC as rim cylinders for exit devices, including Von Duprin, and as disposable or refundable construction cores. Browse SFIC and LFIC cores and the matching IC housings.

What is an LFIC core?

An LFIC is a large-format removable core whose size and shape depend on the lock manufacturer. It uses larger 0.115 in pin segments and a larger body than SFIC. Locksets are built around one maker's LFIC format, so a Yale LFIC core will not fit a Schlage LFIC housing.

The main reason to stay on LFIC is continuity: you keep the existing key system and add mechanical or electronic devices from the same family. Schlage, for example, offers LFIC cylinders in Sargent and Corbin Russwin formats so those locks can move to Everest 29 keyways without changing the lock.

What is the difference between FSIC and LFIC?

FSIC (full-size interchangeable core) is Schlage's name for its own large-format core. Schlage describes its LFIC cylinders for Sargent and Corbin Russwin locks as the competitive equivalent of its FSIC format. In practice, FSIC is Schlage's LFIC, and it does not fit SFIC housings.

Can you mix SFIC and LFIC in one system?

No. The housings are different sizes, so a core cannot move between formats, and Schlage states that SFIC and FSIC cylinders cannot be keyed into the same system. If a campus has both, treat them as two systems: separate control keys, separate core stock, and labeled housings so a tech never reaches for the wrong core.

Which format should you buy?

• Buying new locks or retrofitting mixed hardware: SFIC. It is standardized across brands and the housings are widely available in mortise, cylindrical and rim styles.
• Adding to existing Sargent, Corbin Russwin or Schlage FSIC locks: match the installed LFIC format so existing keys and the control key keep working.
• Rim cylinders on exit devices: SFIC rim cylinders are commonly used on Von Duprin and other straight-cam devices.
• Not sure what you have: pull one core with the control key and send us the brand and keyway, or check the lock's model number. Our team can identify it by phone.

Housing type matters as much as core format. See IC housings explained: mortise vs rim vs key-in-lever for how housings differ, and commercial key blanks by brand for matching blanks. Compatible locksets include the Schlage L9050B 07L mortise lock for SFIC and the Schlage 80-129 SFIC rim cylinder housing. For mortise locks, also see mortise locks.

FAQ

Is SFIC or LFIC more secure?

Format alone does not decide security. Security depends on the keyway (open or restricted), pin count, and any added protection such as a check pin or high-security keyway. Pick the format that fits your locks, then choose the keyway to match your security need.

Are all SFIC cores interchangeable between brands?

The format is standardized, so an SFIC core from one maker fits another maker's SFIC housing. The keyway still has to be combinated for your system, and restricted keyways (such as Schlage Everest 29R) are available only from that maker.

How does the control key work?

A control key operates a separate shear line that releases the core from the housing. You pull the old core and insert a new one without disassembling the lock. Both SFIC and LFIC use control keys, so limit who holds them.

Can I retrofit existing locks to interchangeable cores?

Often yes, if a core housing exists for your lock. SFIC has the broadest choice of housings. Send us the lock brand and model and we will confirm the housing.

Official sources

Format details in this article are drawn from Schlage SFIC cores, Schlage FSIC and LFIC cores and dormakaba 6CS and 7CS SFIC.

Next step

Shop interchangeable cores and cylinders and key blanks. Orders placed before 3:00 p.m. ET ship the same business day after card approval, with free ground shipping on orders of $450 and up. For quantity pricing, use get a quote or call 718-814-6300. Government and school POs go through submit a gov PO.