They are flap closure like blades67 said.
The bandoleir is all you need if you are just going to the range.
I only had luck with PMI's 30-rounders that came straight from the factory. In 10-rounders I always had to bend the lips and install new factory Ruger followers sold by Brownell. The magazines(Triple K, John Masen, and other Unknown brands) never worked for me, until I did the adjustments said in the sentence before. I even heard that a guy from Canada, nameless obcourse, fooled around with the Triple-K's magazines and made them 15-rounders. He metioned that he shaved the bottom of the follower and bended the lips of the magazine. No one else has try this, so we do not know, if this really works. And if you live in the U.S. this is a ATF/DOJ no,no. So do not try-it it is extremelly illegal.
~>TCW, Email me.