8mm
i think they are external torx
around 8mm, if we consider carbon steel 516-70 service material to be steam....
To convert 516 to percent multiply by 100:516 × 100 = 51,600 %
516/1
516
516
516-434 = 82
It is: 516 = DXVI
516 since 516 is a multiple of 4 (129x4=516)
827 - 516 = 311
5/516 = 0.00969