We had a customer who ordered four shades all at the exact width even though the sizes were slightly different. In most cases, up to 1/2 difference will still allow the blind to hang properly. When it comes to roller shades though, measurements are crucial. For all of our blinds and shades, each window needs to be measured individually. Never assume they are all the same. For roller shades, the fabric is actually narrower than the the entire shade. It has to be made that way because the material is on the roller. The only place to install the mechanisms and the brackets is from the sides which adds width. There is a 1 3/8″ to a 1 1/2″ difference between the fabric and the mechanisms. Our factories know this so normal deductions are very slight. In most instances, if the roller doesn’t fit snug from a side mount, changing the brackets to an up mount and bringing them in is all it takes to make it work. Our installers actually up mount all roller shades when that option is available. In this particular instance, the windows were old and the was no place for an up mount. The only solution was to reorder the shade wider or come up with another alternative. The customer chose to use shims to pull the brackets closer to the pins. We used clear plastic shims normally provided for a cassette option. The end gets wider like a wedge and as it is pushed down it pushes the bracket closer to the pins. Screws hold it in place.