In reply to paul mitchell:
The raison d'etre for the chromemolly piton Chouinard produced was that they could be placed and removed over and over and over again. This was at a time when various European climbs had become basically via ferrata with pitons from bottom to top, and Chouinard's vision was a climb devoid of hardware that would present the same challenges to subsequent parties that the first ascent party had faced. At the same time, he realized that the hodge-podge of European piton shapes was ill-suited to the regularity of Yosemite cracks and to the needs of efficiency on big walls, and so created a graduated sequence of standard sizes that, once learned, often made piton selection automatic.
What Chouinard didn't forsee was that Yosemite climbing would become so popular that the continual placing and removing of pitons would alter (in some cases grotesquely) the very environment he thought he was striving to preserve. His response was to undermine his own very successful piton business by making and aggressively promoting stoppers and hexentrics, which of course wouldn't damage the rock. Of course these had been in use in the UK for years, but the idiosyncratic selection of sizes and shapes, perhaps well-suited to British cragging, wasn't very effective on Yosemite's wide range of uniform cracks, in the same way that European pitons were suboptimal. (Given that all manufacturers have adopted graduated standardized sizing, it seems clear that Chouinard understood the technical protection demands better than his contemporaries.)
