apart from 4mm whats the difference between 16 & 20mm pots?

[Coolhand78]

with respect to putting them in pedals?

[Lee]

Well yes the size I prefer to work with bigger pots. Smaller ones seem to look funny in a large enclosure but if your using a small enclosure like say a Sonic Titain size then the smaller ones work best. Large enclosure larger pots smaller enclosure smaller pots. Sound wise they should be the same.

[Dr Tony Balls]

no difference. certain brands might have different audio tapers than another, but thats about it.

[Coolhand78]

awesome, thanks fellas.

[PlumCrazy]

There might be a wattage difference but shouldn't be a factor with 9-18v.

[sir h c]

Another thing to remember is that there is not an infinite resolution on a pot. There is some limit to the ability to step, so the smaller the pot usually the lower the resolution (not that you would notice, but if it is for really tweaking it might be enough to care).