This is a reducer for 100mm to 70mm pipe that fits the TwoTrees Laser enclosure that is 780x720x460 as pictured here.

You can use the original screws that came with it if you wish, but if you are deleting the ridiculously tiny fan (keep the fan guard, it will stop stuff flying up into the pipe) it's much easier to use some smaller M4 screws, washers and nuts.