Different pew cages fasten on to the arms and backs of pews depending on their style. Always take care to protect the wood finish of the pew if necessary.
The largest pew hanger has a round cage that snaps into place - no cutting of foam is necessary. The small cage being shown in this demo has two styles of clips - one that locks over the top of the arm and one that clips from the side.
For this demonstration, I'm using this pew clip that slides on from the side. Cut the foam and fit into the box. The sides are all open for easy insertion of greenery and flowers from the sides, bottom, top and front.
It takes very little foam for an arrangement with 5 - 6 flowers. Just remember that water evaporates quickly in open cages like this. The water in the arrangement may need to be replenished before attaching to the pews.
You do not want it "dripping" right before placing it on the wood arms!
Here's a closeup on how this style clip attaches to the arm of the pew.
You are ready to begin inserting greenery in the foam for your design.