Designed to fit 'KONIZY' refills from Amazon, which are 100mm long, with an opening that is 38mm wide. I believe this means it will fit most standard refills, Ikea and most Scotch-brite included, though I would measure first. 

(EDIT: It seems that some scotch-brite refills have a larger opening, and no cardboard core. I may add a variation to support these in the future, but for now you should probably skip printing this handle if you want to use that type of refill. Thanks to user NeverEnoughInk for the heads up!)

While most other handles on here are printed vertically, this one is intended to be printed flat, with 0 top and bottom layers. This results in a fast, but sturdy print. The examples in the photo were printed with 3 0.6mm perimeters and 9% hexagon infill. They are more durable than they need to be, so there is room to reduce that even further.

Top portion is split, so that it may compress while loading and unloading a refill.

The top is also flat, to allow the handle to be rested on its end.