These are considerably stronger latches than the simple bullet type, although they function in much the same way. In this case, two balls snap over a keeper (or strike) with adjustable pressure, allowing variable spacing between the balls. This adjustable spacing lets the keeper enter the catch from the front or either side, making it usable on overlay or inset doors.
Size stated is the overall height by width. The 38mm × 7mm, 43mm x8mm and 50mm × 9mm catches require #4 screws; the 60mm × 11mm and 70mm × 13mm catches require #5 screws (not included).