Jul 29, 2009 · Rotating Pipe Flange Bolt Holes to Straddle a Vertical Center Line GT By Gene Teichroeb 07/29/09 For example, let us say that you have an existing pipe route with an 8-bolt-hole pipe flange straddling the vertical center line at one end, and you want to start a new pipe route, beginning with a matching 8-bolt-hole pipe flange to be bolted to ...