Actually, on the ChipGuide we typically identify these types of Plain mold chips as Small Circles (SmCirc) Mold. The mold category is reserved for Plain mold chips that have those record-like concentric grooves (wide groove, narrrow groove, or ledge and groove). There are currently about 100 chip entries that have that designation on the ChipGuide. There are likely others that are still mis-labeled as Plain mold. The challenge with these chips is that unless the ChipGuide photo or scan is high resolution, it is difficult to see those grooves, and they are simply designated as Plain Mold chips. The ChipGuide "Saw Tooth Club" chip scan was such low resolution, it was almost impossible to see the grooves. (Fred, can we upload your much better scan?)

Here are some more examples of the mold category. I just picked some of the better ChipGuide photos/scans that show that clearly show grooves;

The mold was an open mold, sold by the Burt Co. to several gambling supply distributors, including Frank Walters Precision Dice (Detroit, Michigan) and T. K. Specialty (Kansas City, Kansas) in the 1940s and 1950s.

I suspect that most of the SmCirc mold chips with the unusual rim hot stamps were made by the Salt Lake Card Co (Salt Lake City, Utah), a gambling supply distributor owned by Edward (Jimmie) Stroud from about 1949, until his sudden death in 1958. As visible in the sample chip below, Stroud specialized in hot stamping inside of the groove of these Small Circle Mold chips. I imagine that this involved some patience and a lot of precision.