The Particle V1 replacement knobs are available from Mouser, eBay, and other sources.  The knob has a set screw and 6.4mm (0.25") shaft hole.


KnobDiameterSCI Part #Alt Part #
Mouser Part #
Large (mode switch)
20 mm (0.77")PN-8EPN-38C
Eagle 450-2035-GRX
Small (potentiometers)15 mm (0.59")PN-8FPN-38D
Eagle 450-2034-GRX