Latin suffix -klo- > -culus, origin?

What's the origin of -k- in diminutive suffix -culus (<*-klo-)? It was frequent in n-stems and s-stems, and even r-stems:
homo, homunculus
portio, portiuncula
carbo, carbunculus
mas, masculus
*crepus, crepusculus
opus, opusculus
mus, musculus
os, osculus
corpus, corpusculus
frater, fraterculus

Is it from names like *ox, oculus (*okWs, *oKw-lo-) ?