Why won't Apple Store give me back my battery screws?

I brought my 15" macbook pro (2011 not under warranty anymore) to an apple store to get my swollen battery checked out. They disposed of the battery and I decided not to get a new battery. A week later, I get a call from the apple store telling me that they forgot to put the battery screws back into the laptop while they disposed of my battery and they told me to go pick them up. So when I went in to pick up the screws (I didn't bring the macbook) they told me they can't give me the screws because :

1. They can't give it back to me unless they are the ones to install it to the macbook to avoid damage

2. The screws require a special screwdriver and I wouldn't be able to use it myself anyways

I told them I just wanted my screws back for a $2400 laptop I purchased (again, it's not even under warranty anymore, so any damage I do to it would be on me anyways) and I didn't need them to install it back for me. The rep refused me stating the same reasons again and started giving me attitude at this point. They also told me if I don't come pick them up (with the macbook this time), if someone else needs the screws, they will give it to them. It was clear that the rep had no intention on giving me back my screws. So I backed off, and left the store.

It seems like they're just trying to make it really hard for me to fix my own laptop so I would just buy their battery replacement service. Are those screws not my property? Why won't the Apple store just give me back my battery screws for a mistake they made on their end?