Grex A150029 - Piston Grex from $2.26 $2.75 Qty. Add to Cart SKU: GRX-A150029 This item is currently on backorder but you can still purchase it now and we'll ship as soon as more become available. Genuine Grex replacement part A150029 - Piston. For Grex Models XB, XBi. Chart referance number 17. Tweet