Lockstrips are soft metal that rolls into the rubber window gasket that once the lockstrip is installed the gasket tightens to the glass and window frame. In the rear of the window corners are little separate corner pieces because the metal will not bend around corners, you can buy the lockstrip rolls off of ebay but the corner pieces you cannot and most of them are rotted out to begin with, so if yours are in good shape don't do what i did and throw them away (i was unaware of what i did at the time) . i have looked for some for two years with no luck. If your window guy trims the lockstrip roll carefully you really do not need them unless doing a serious restoration but i like to try to keep as close as possible when i can. if you are buying a complete car it will have them, just dont dig out the gasket without trying to save them.