A lock comprising: a housing having an inner surrounding surface that defines an inner space; and a cylindrical core body having a lock axis, said core body being substantially mounted in said inner space, and being rotatable relative to said housing about the lock axis, said core body including a core axle that extends along the lock axis, and a core tube that is sleeved on said core axle; wherein: said core axle has a plurality of helical keyways that are formed in an outer surrounding surface thereof and that extend about the lock axis, each of said helical keyways extending through an end surface of said core axle to form an insertion opening; and said lock further comprises a plurality of tumbler units each including a housing pin hole that is formed in said inner surrounding surface of said housing, a tube through hole that is formed through said core tube and that is in spatial communication with a corresponding one of said helical keyways, a pin assembly that is movably mounted in said housing pin hole and said tube through hole, a hole-defining surface that defines said tube through hole, and a resilient member that is disposed in said housing and that resiliently biases said pin assembly toward the lock axis, said hole-defining surface of each of said tumbler units having a shoulder surface portion that faces away from said core axle, a portion of said tumbler units serving as coplanar tumbler units that respectively correspond to said helical keyways and that reside in a first plane perpendicular to the lock axis; wherein, when said core body is at a latching position relative to said housing where said housing pin hole and said tube through hole of each of said tumbler units are aligned with each other, said resilient member of each of said tumbler units resiliently biases said pin assembly to abut against said shoulder surface portion and extend into a corresponding one of said helical keyways through said inner surrounding surface of said housing. a housing having an inner surrounding surface that defines an inner space; and a cylindrical core body having a lock axis, said core body being substantially mounted in said inner space, and being rotatable relative to said housing about the lock axis, said core body including a core axle that extends along the lock axis, and a core tube that is sleeved on said core axle; wherein: said core axle has a plurality of helical keyways that are formed in an outer surrounding surface thereof and that extend about the lock axis, each of said helical keyways extending through an end surface of said core axle to form an insertion opening; and said lock further comprises a plurality of tumbler units each including a housing pin hole that is formed in said inner surrounding surface of said housing, a tube through hole that is formed through said core tube and that is in spatial communication with a corresponding one of said helical keyways, a pin assembly that is movably mounted in said housing pin hole and said tube through hole, a hole-defining surface that defines said tube through hole, and a resilient member that is disposed in said housing and that resiliently biases said pin assembly toward the lock axis, said hole-defining surface of each of said tumbler units having a shoulder surface portion that faces away from said core axle, a portion of said tumbler units serving as coplanar tumbler units that respectively correspond to said helical keyways and that reside in a first plane perpendicular to the lock axis; wherein, when said core body is at a latching position relative to said housing where said housing pin hole and said tube through hole of each of said tumbler units are aligned with each other, said resilient member of each of said tumbler units resiliently biases said pin assembly to abut against said shoulder surface portion and extend into a corresponding one of said helical keyways through said inner surrounding surface of said housing. said core axle has a plurality of helical keyways that are formed in an outer surrounding surface thereof and that extend about the lock axis, each of said helical keyways extending through an end surface of said core axle to form an insertion opening; and said lock further comprises a plurality of tumbler units each including a housing pin hole that is formed in said inner surrounding surface of said housing, a tube through hole that is formed through said core tube and that is in spatial communication with a corresponding one of said helical keyways, a pin assembly that is movably mounted in said housing pin hole and said tube through hole, a hole-defining surface that defines said tube through hole, and a resilient member that is disposed in said housing and that resiliently biases said pin assembly toward the lock axis, said hole-defining surface of each of said tumbler units having a shoulder surface portion that faces away from said core axle, a portion of said tumbler units serving as coplanar tumbler units that respectively correspond to said helical keyways and that reside in a first plane perpendicular to the lock axis; wherein, when said core body is at a latching position relative to said housing where said housing pin hole and said tube through hole of each of said tumbler units are aligned with each other, said resilient member of each of said tumbler units resiliently biases said pin assembly to abut against said shoulder surface portion and extend into a corresponding one of said helical keyways through said inner surrounding surface of said housing.