2001 Warning Track is an insert set in 2001 Studio. All three variations were randomly inserted into packs. The base 34 card set that consisted of great sluggers and pieces of the walls from various stadiums, primarily Three Rivers Stadium that was home field of the Pirates prior to their new PNC park. Note – Card #26 Hank Aaron does not exist in the set and Card #28 Roberto Clemente is short printed. None of the cards are serial numbered.