H136758 Combine Grain Head Wobble Box Arm Fits John DeereOne New Aftermarket Replacement Grain Head Wobble Box Arm Fits John Deere 900 Series Flex Head Platforms This aftermarket replacement wobble box arm (also identified as a sickle knife drive Fits Case arm) is a key component of the grain head wobble box assembly on Fits John Deere 900F Series flex head cutting platforms. The wobble box converts rotary input from the combine drive system into the reciprocating motion that drives the sickle knife bar,