A lock assembly includes a coupling mechanism connected to a spindle assembly. The coupling mechanism has an outer sleeve having a longitudinal interior opening that extends along a first axis. An operator handle includes a proximal lock core opening, and a distal shaft portion having an axial opening configured to receive the outer sleeve. The distal shaft portion and the outer sleeve are configured to define a through path oriented across the longitudinal interior opening of the outer sleeve. A portion of the through path at the outer sleeve is configured to threadably receive a setscrew to fasten the operator handle to the outer sleeve. A keyed lock core has a tailpiece that is positioned in the longitudinal interior opening of the outer sleeve to obstruct the through path and block access to the setscrew via the through path to prevent unauthorized removal of the operator handle.