These are extra heavy duty stainless steel jump rings. This assortment includes some heavy, extra heavy and ultra heavy thickness jump rings to give you a variety of thick rings to choose from, for heftier pieces.

Included sizes are
6mm and 7mm in 16 gauge (1.2mm thick),
8mm, 9mm and 10mm, in 15 gauge (1.5mm thick) and
13mm and 15mm in 12 gauge (2.0mm thick).

This assorted kit contains all of these sizes (they are also sold separately in a separate listings).

These are very thick and are not opened and closed easily. Pliers heavy enough (and hand strength) are needed. I personally use

Made of 304 grade stainless steel. Non tarnish and hypoallergenic.

Contains about
150 pieces 6mm,
125 pieces 7mm,
75 pieces 8mm,
60 pieces 9mm,
50 pieces 10mm,
20 pieces 13mm and
15 pieces 15mm.
I do not count them as I make every kit. I just fill the bins as much as can fit. I have found that it's turns out to be about these amounts.