This thing creates a customizable dovetail joint when can be used to securely joint two different pieces.

The definitions of the parameters:

Pin Depth : the depth of the Pin from the start of the chamfer to the widest part of the pin
Pin Width : the width of the widest part of the pin
Tail Height : the height of the tail block
Pin Width Fraction : 1 minus the ratio of the narrowest part of the pin (start of the chamfers) to the widest part. A value of 0.4 would result in the width of the narrowest part of the pin being 60% of the widest part
Pin Height Fraction : the ratio of the height of the pin to the height of the tail block. A value of 0.8 would result in the pin being 80% of the height of the tail block.
Overhang Depth : additional depth added to the narrow end of the pin and the back of the block
Overhang Width : additional width added to the tail block on each side of the pin chamfers
Fit Tolerance : the absolute value of the total amount to shrink the width and depth of the pin so that it will slide into the tail
Corner Trim : the absolute value of the amount of material to remove from the edges of the widest part of the pin to make the pin slide comfortably into the tail without having to drastically increase fit tolerance.
Pin Or Tail : make the pin, tail or both

Best bet is to experiment with different values to see how the joint changes. The fit tolerance and corner trim works well for me for my printer and PLA - a tight fit but no filing necessary. For ABS slightly lager values of Fit Tolerance and Corner Trim are needed to get the pin to easily slide into the tail. Alternatively for ABS, I just file a little bit off the sides of the pin and it usually slides snugly into the tail.