Thin prongs at heel:

A prong that is thin at the heel will catch, bend, and break easily. This prong will never stay tight.

 Thin prongs:
A jeweler who carelessly polishes the ring can remove too much gold. Prongs with this problem can break or wear off in a short period of time and result in the loss of the diamond.

 Hooked prongs:

The prong seems tight at first, but in a short time it will loosen. This type of prong will break and you'll very likely lose your diamond.

Prongs lacking bearing:

With too little support beneath the diamond, the stone can tip and become loose in the mounting. 

 Prongs not secure on the surface of the stone:

This prong looks for threads to catch on and nylons to ruin; anything with fiber is its prey. This type of prong is an enemy of good clothing.

Prongs cut with a saw:

This is a quick way to set a diamond and an even faster way to lose it because the prongs are too weak to last.