Stops can be made is various diameters to accommodate various mesial-distal widths. For example a lateral incisor width is much smaller than a molar.. The larger the outside diameter the larger the drill can be compatible with the stop.
The smallest diameter stop is 3.5mm OD. This diameter will allow up to the SD 2.8 and is used for lateral incisor and lower anteriors.
The most common is 5.27 mm OD and can be used in 90 percent of the cases and will accommodate up to the SD4.8
The largest diameter stop is 6.0mm and will accommodate up to SD 5.4