I apologize for the delay in my response to this subject. Nonetheless, here they are. There are six of the round ones, two in each size. They are essentially big heavy washers. On the bottom, they have plastic covers with three slits extending to the edge, where you can insert a flat thumbtack. I found these in my Mom's old sewing kit, and begged her for them. This was before I even understood exactly how valuable they would be to me. I love them.
I have seen the yellow ones that were posted in a previous entry, and they are designed to function similarly as mine. However, I don't believe that the spikes can be removed. Also, they aren't quite as simplified. The plastic is a hard case with a weight inside, which is kind of loose and rattly. Also, they have little ridges built into the top so that they can accommodate each other's spikes when stacked. All of this seemed a little excessive to me. However, all and all, they do seem like a good option compared to the other kinds of weights that are readily available.
I also recently purchased this iron from goodwill. It is seven pounds, but pretty small. It is great to have around to really anchor something down. I plan to get more as I see them. They are perfect as pattern weights. They are also readily available and inexpensive.