Chainsaw Repair

They will go through but it does take a big effort.  As noted, lube it well and try "folding" the flange and poking one side through then grab it with a pair of needle nose pliers and pull it through. 

Be careful that the "flange" thickness matches the one you took out, the older ones had a thinner flange and the later ones have a thicker flange.  The gaskets are different thickness as well so the flange, gasket, even the disk changes over time.  The older ones had the thin flange, thin gasket, and the phenolic disk.  Later ones have a thicker flange, thicker gasket, and thinner aluminum disk. 

With the wrong combination in there, the disk will never unseat and won't allow the pump to pull oil from the tank.

Mark