Pictures of "Theta" Maille
These rings are from a coif of possibly Turkish origin. It is likely a 17th century or later specimen. The solid rings in this garment are evidently forge welded. I base this on the fact that on many of the rings you can see the outline of the wire due to incomplete welding. Also interesting about this garment (and the associated hauberk) is that some of the solid rings have a cross-bar integral with them, making them resemble the Greek letter "theta". Hence the name "theta maille".
A fully intact theta ring: