two holing a flange two holing a flange lelia (Industrial) (OP) 26 Jul 03 23:01 correct procedure when two holing or allignment of welded flange RE: two holing a flange rhodie (Industrial) 28 Jul 03 12:38 Your post might be a great question, but it isn't.What exactly are you asking?(I'd bet your answer depends upon the concentricty tolerance on whatever part drawing you are talking about.) RE: two holing a flange unclesyd (Materials) 3 Oct 03 22:39 A little late.To two hole a flange means to have the two top holes of a flange straddle the vertical centerline of the flange. This is easily accomplished using two pins that fit the bolt hole and make the pins level while still straddling the vertical center line. This can be accomplish by experienced people with just a level lined up with the top or bottom of bolt holes. This method is very accurate. If a single bolt hole straddles the vertical center line is said to one holed. This method is hard to do in the field.Using the two hole is mainly for allowing individual piping spools to line up when assembled. There are other reasons, like inserting a gasket by removing fewer bolts.