I have that circle cut ruler for years and my 18 mm didn't work on either and I also was not aware that there was a special rotary cutter for it i look on the instructions dosen't say anything either and fons and porter just this morning had circle makeing quilts and use that ruler they made no mention of of the special cutter.I got the circle cutter ruler hopeing it would easier then the olfa circle rotary cutter a pain in my rear i just couldn't get the hang of it I am now going to google the cutter see what i come up with