Spring-loaded camming devices were developed to protect perfectly parallel-sided cracks that could not be protected with traditional chocks. Cams have come a long way since the early versions of Wild Country Friends. Modern units are lighter and stronger and reverse strength is now standard on almost all devices after being introduced first by Black Diamond and then HB Climbing Equipment of Wales.
British manufacturers (Wild Country, DMM and the now defunct HB) use a fairly consistent system of sizes ranging from 0 or 00 to 6, but international manufacturers generally have their own systems. The most generally useful sizes to start with are DMM 1, 2 and 3 (or Camalot 1 and 2). Sizes 5 and 6 are rather specialist and only really useful for big offwidth cracks on grit or granite.
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