Parameters include top part diameter and height, bottom part diameter and height, knurling radius, count and pointiness, bolt diameter and hex head size and depth.

I have use this so far to make knobs for a 1/4" bolt and an M4 screw (pictured). The M4 has the pointiness dialed down and the head is proportionally larger to provide a bit more torque. But you can make it whatever you like.

One STL file is for a 1/4" hex head bolt - I used this on a tripod head. The other is for an M4 screw. To make different knobs, grab the SCAD file and twiddle away with the parameters.

This prints upside down so a bridging layer is printed between the hex head and the shaft cutout. It is possible to print without that support layer but it doesn't come out as nice. Just cut that out with a knife or a drill and you're ready to go.