Organ pipe stoppers for busker organ - parametric

I am building from plans a 20-note busker organ, from a well-known design. The organ's flute pipes are tuned by sliding tight-fitting stoppers up and down inside the top of the pipe. The creator made his stoppers from wood, I wanted to print mine because my wood cutting skills are not great.

Not all my pipes turned out completely square so my OpenSCAD code allows the creation of trapezium-shaped stoppers. It's probably better to remake the wonky pipes properly, and I may do that later, but for now I'll make stoppers to fit what I've got. 

The OpenSCAD code allows the user to specify all the variables including thickness of the stopper base, height and diameter of the grip, whether to have a knob on top of the grip, and more. The crucial ones are the dimensions (if a rectangle, you only need enter two lengths; if a trapezium enter 3 or 4) and the thickness of the leather that will seal the stopper.

I've included .stl files for most of the stoppers that are in my organ's pipes. The OpenSCAD code is very easy to alter to suit your own needs. There's a diagram showing which dimension applies to which side in the code. The parameter descriptions are at the top of the code.

So far I have not accidentally broken any of the stoppers, even though there is a risk that forcing the stem sideways might cause a snap across the layers. The risk can be reduced by using more infill than my 10%. A dribble of superglue around the stem seems to make the grip really tough and hard to break.