All three ready-made libraries (Ph.D.-7, Ph.D-12 and Ph.D-C7C) may contain binders to a given target. Choice of library is not dependent on target-type or downstream application. For this reason, we recommend that most customers start with either of the two linear libraries, Ph.D-7 or Ph.D-12. The exception is when a looped structure is necessary for the application, in which case the disulfide looped Ph.D.-C7C library is recommended.