This is an Alpha W Taper pot, as used in the Tube Screamer and other circuits like the GuitarPCB SuperSonic-02. The W Taper has an audio (logarithmic) curve to the halfway point, and then switches to a reverse-log (or anti-log) taper from the middle to the end. So the adjustment is aggressive for the first third, flatter for the middle third, and then more aggressive toward the end of the rotation.
This is a 16mm diameter solder-lug potentiometer with a 15mm shaft length (including threads) and 6.35mm (1/4 inch) diameter shaft. The threads are 6.5 mm long, and the section of the shaft extending beyond the threads is 8.5 mm.