Stockwell is an active midrange EQ that provides approximately 15 dB of gain or attenuation between 200 Hz and 8 kHz.
This kit contains all necessary parts, except the pcb: Parts list
You can order the pcb form Kurt Ballou: God City DIY PCBs
Knobs for the pots are not included in the kit, you can select them yourself. The 2 pots have round 6.3mm shafts.
Here´s the build documentation: