For tensioning the chain and changing the chain, bar and spark plug. Width across flats: 19 (for MS 261 up), 19-13 (for MS 271, MS, 291, MS 311, MS 391), 19–16 (for MS 170, MS 171, MS 180, MS 181, MS 193 C, MS 211, MS 231, MS 241, MS 251), 16 and 13 ( for MS 150, MS 201, MS 201 T).
