THPI-400 Thomastik Infeld Peter Infeld cello string set 4/4 medium THPI-41 Thomastik Infeld Peter Infeld cello string A-1 4/4 medium THPI-42 Thomastik Infeld Peter Infeld cello string D-2 4/4 medium THPI-43 Thomastik Infeld Peter Infeld cello string G-3 4/4 medium THPI-44 Thomastik Infeld Peter Infeld cello string C-4 4/4 medium