Thick or regular, what is the difference, and why are there both options?

There is no halachic difference between thick or regular strings (both are “kaful shemona” eight strands wound together by “shezira”) – the only reason we supply both is that some people like the way the thick look on their talit (especially the talit gadol) and others find that the thick last longer since they tend to withstand tugging and snaring that sometimes tears the thinner strings.

– Mois Navon.