If you were using the stock AfterShock hexes then even the LST2/XXL hexes would be an upgrade, or 17mm buggy hexes. I would guess 17, 20, or 23 hexes would hold up fine on the MMM, I used stock LST2 hexes with a NEU 1527 and they held up fine.
anything 17mm or bigger will work just fine. 14mm is too small.
They say a good mechanic only needs 2 tools - WD40 & Duct tape. If it moves, and its not supposed to, duct tape. If it doesn't move, and its supposed to, WD40.