Metal knurled knobs were used on JMI (British) and a few Crucianelli and Eko (Italian) built Vox guitars between 1963 and 1967. These knobs did vary to some extent, and how much of this was deliberate, and how much a function of being hand-turned in different locations is unclear.
This image shows four subtley different Vox metal control knobs, from 1) 1966 Vox Symphonic bass 2) 1965 Vox Ace 3) 1967 Vox Mark VI special 4) 1966 Vox V232 Violin bass - all given part number 09-314-0. As can be seen there are differences in height, width, marker dot size and position, underside, and knurl pattern. The first three knobs were all fitted to British (JMI) guitars, the last to an early Italian (Eko) model. Although hard to see here, the knurl pattern on this last knob is inverted - see the fourth image - the diamond shape is depressed rather than protruding. Each of these knobs is described in greater detail below.
image 1 Control knobs from a 1966 Vox Symphonic bass. The pickup selector knob arm simply screws into the grub screw hole of the regular non-arm knobs. Dimensions: height 15.5mm; width of base 22.3mm; width of knurl 16.9mm. The grub screw is hex key type, 2.7mm x 3.4mm.
image 2 Control knobs from a 1965 Vox Ace. Dimensions: height 15.6mm; width of base 22.2mm; width of knurl 16.0mm. Hex type grub screw, 2.5mm x 3.4mm.
image 3 Control knobs from a 1966 Vox V232 Violin bass (solid body). Dimensions: height 15.9mm,; width of base 21.9mm; width of knurl 15.4mm. Slotted grub screw (as opposed to the hex screws of all the above examples), 3.1mm x 6.1mm.
List of Vox control knobs