Thomas Grinding Stump Eater stump grinding attachment comes in models SG110-32 and SG110-44. Self-powered units attach to excavators and use a Sandvic Dura Disk II cutting system. On the larger SG250-44, disc speed is 420 rpm with engine speed at 2,200 rpm. On the smaller unit, disc speed is 487 rpm at 2,200 rpm.