What's this about?
Some office chairs have the back rest attached underneath to the seat bottom using a curved piece of steel with 2 bolts.
Style #3318 has the 2 holes predrilled.
If purchasing stye #3323, the holes are not predrilled.
You will not have to drill these holes if the back is attached to the seat.
To drill these 2 holes, trace the hole location from the old mechanism and drill the same size hole.
We suggest when drilling and for safety, place a 3/4" thick wood board under the mechanism for when the drill point goes through the metal. It will grab! Drill slowly and a few drops of oil while drilling is good.