It isn't custom made parts, they are mass-produced reinforcements for your TM SR-10 or for your JG BAR-10.
We produced the piston from three different material. The body was made from high strengt, alloyed aluminium. The back-part connected with glued screw-thead and it was made from high strenght stainless steel and at last, we placed "plastic" spacers on the piston to reach the really smooth movement in the cylinder. This parts tested and it won't be never worned, we haven't any replacement issue in the past (even after 10 year of use). We recommend to use it with our own parts for the best performance.