Theres also a casing whell...they work well..once!
Whatever and however your cutting you must have a sharp blade...dont bother with stanley knifes, one you have made a couple of cuts the tip of the blade wont be sharp enough,
Go for snap off blades, I find the 9mm once better that the bigger 18mm
If im not mistaken that triangular tool Sonny mentioned takes the smalled blades.
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