Marks Euro Profile Double cylinder lock for 2750 Thin line Security Door mortise lock.

Cylinder Type: Euro Profile, Double Cylinder - Key both Sides
Length: 2-3/8 inches (60 mm)
Color / Finish: Satin Chrome or Satin Brass
Rekeyable: Yes
Keyway: Schlage 5 pin SC1
Priced and sold each.

Note:
Standard keyway, Marks A standard 5 pin Kwikset KW-1 key
Optional Keyway: Marks C Keyway = 5 pin Schlage SC-1 key

Terminology-
Single Cylinder: Key lock may be locked or unlocked with a key from the outside. The thumb turn allows locking or unlocking from the inside.

Double Cylinder: Key operated from both sides of lock. Locking and unlocking can be accomplished only with a key. Used in situations where free egress from the inside is not needed or desired.
Note: Some cities have codes that do not allow this type of lock - Check your codes