This set of sliding window latches includes two front and two rear sliders along with all of the hardware to mount them. Often the original latches get seized or break, or they no longer lock the windows in the rail, so upon a hard stop or launch they slide around.
 
Early 59-64 Mk1 models used metal latches, however they are very expensive and stock is not consistent, so these plastic latches can serve as replacements with the correct rails.