600mm manhole cover YAC With or without pressure Size: 350*90mm 20 years specialized manufactuer Type:Squareness,Roundness,Oval,Hand Hole Cover Material: ... 304,316L,321,304L,316Fineness: inner and outer fineness of mirror Ra≤0 ... .8μm,inner and outer mechanical polish and electrical polish Ra≤0.2μm,external surface ...