1968-1973 Beetle Rear Wheelhouse and Bumper Bracket Retainer Panel LH measures 19 x 10.5. This is the inner panel that your rear bumper bracket is mounted to for correct bumper mounting.
Learn more from the following Mid America Motorworks Knowledge Library articles:
1949-1979 Beetle Fender Identification Chart
VW Beetle Fender Removal and Replacement
VW Body Panels & Sheet Metal - What to Expect
Klokkerholm