Here is and excerpt from an article about Kretchmer tension settings:
in Kretchmer's designs the equivalent of 12,000lb. per square inch of metallic, springy pressure. Few gems (only those scoring 9 (out of 10) or higher in the hardness scale such as Ruby and Sapphire) can sustain this enormous pressure, first among which is Diamond, the gem of highest hardness (10 out of 10). The exerted pressure guarantees, further, safe setting for longer than a lifetime.
and more
Despite the appearances of "floating in mid air", the mounting is stronger than most conventional prong and bezel settings which tend to loosen with time and use (it enjoys, furthermore, the added benefit of eliminating the unnerving entanglement of prongs in fabrics...). This due to the treated metal springiness and to the fact that more surface is touched by the setting but at points that are optically less critical in terms of exposure of beauty, brilliance and wholesomeness of the Round Brilliant shape: Kretchmer settings hold their diamond solely by its girdle.
The aging and seasoning of the treated metal in Kretchmer's studio furnaces prevent the brittleness that precious metals develop over time and guarantee the treated metals longer endurance and longer retaining of their finish than their standard, untreated 'equivalents'.
Statistically, practically and mechanically speaking a Kretchmer tension setting will never loose its diamond. Only through the use of specialized tool may a Diamond be de-mounted from those settings. Similarly, Kretchmer rings can be set and mounted only in Steven Kretchmer's studios.