Pressure-mounted gates are most flexible and don't take screws. If it is important to be able to move the gate frequently or if you are unable or unwilling to put any screws into the doorways you wish to barricade, choose a pressure-mounted dog gate. However, there is a larger assortment of bracket-mounted dog gates.
Hardware-mounted gates take a screw or two but rarely need very much installation. And, although they are mounted with hardware, the manufacturers do their utmost to keep holes to a minimum.
Nearly all gates have a variable width. Our advice is to take the width specified, and subtract an inch. The bar spacing has been developed specifically to confine small pets. There is not a problem with toy breeds squeezing through. In fact, some gates come with tiny doors to allow small pets (usually cats) to pass through while confining the larger dogs.