20 x 20 mm, so for Kosmo modules with mounting holes 194 mm apart that gives 174 mm clearance which is just slightly less than the figure mentioned in the spec discussion:
In practice I’d guess most Kosmo format modules would fit.
Definitely too wide for Eurorack. Personal or other formats, you do the math.
US price is $14/meter for 1 m lengths, plus shipping, and $2.34 for 30 t-nuts.