When you buy the Lee filter holder, you build it yourself to suit your requirements. The width of the slots can be adjusted by fitting thinner or thicker shims. Consequently, most 100mm wide filters can be accommodated. This system also allows the filter holder to be revised as your requirements change.

As I've mentioned in other posts, graduated ND filters 'go-off' over a period of time, depending on the age and the manufaturers QC. Lee stamp the filters manufacturing date on their filters, and, having tried Cokin and Hi-Tech, I've found Lee GND's to be the most consistant and long lasting.