Aftermarket (A/M) parts are NOT made by the original manufacturer; typically they are made overseas and shipped to the U.S. as alternative replacement parts for various vehicles.
In many instances the fit is not as accurate as the “original equipment manufacturer” (OEM); causing lines between the panels to have variances from front to back or side to side.
The finish on the A/M parts is not as corrosive protected as the OEM part. Structurally, most A/M parts are inferior to OEM.
Please refer to CrashRepairInfo.com for all the details.