Vic Firth Corpsmaster Keyboard -- Medium Marimba Cord Corpsmaster Birch Marimba Mallets Medium These marimba mallets feature heavy heads wrapped with a synthetic blend cord (Except for the M72) which provides improved durability and better weather resistance than wool yarn The marimba mallets are constructed with birch shafts These marimba mallets feature heavy heads wrapped with a synthetic blend cord (Except for the M72) which provides improved durability and better weather resistance than wool yarn The marimba mallets are constructed with birch shafts