Made out of Ductile Iron, which expands less than steel, with the same strength as 1045 steel. Machinablility is better than 1045 steel. Easier to achieve higher tolerances, and better surface finishes.
Caps are Taller eliminating the need for girdle spacers. This makes a more ridged and stable combination. Can be used with 14mm studs.
Includes a wider Main cap so a Thrust bearing can be used on the bottom side.
Caps are undersized so main tunnel bore will need bored and honed. Caps are also taller and will need machined / fitted to your girdle