I had a Serpa for one of my HKs. It rattled until I super glued a thin piece of leather in the holster where it meets the trigger guard. That took care of it in my case. That little piece of plastic, Can't tell ya what its for. Never needed it.
The rest of the world gets it,why can't we?
"The United States can survive a Barack Obama,who is, after all, merely a fool. It is less likely to survive a multitude of fools such as those who made him their president".
Out of the Czech Republic