There are two kinds of set on this leaf and they are bought for opposite reasons. A general set covers a size range so that whatever fastener appears, something fits. An application set covers one job completely, and outside that job most of it will never be used. Most workshops end up holding both, one for the unexpected and several for the jobs that repeat.
General sets are read on drive size and the size ladder they cover rather than on piece count, since a set with gaps in the middle is worth less than a smaller unbroken one. Drive size fixes what the sockets will run on, so it is matched to the handles already owned.
Application sets are read on the job. Wheel nut sets at 7 pieces on 1/2 inch drive cover the common nut sizes, with an extractor set for nuts already damaged and a 3 piece alloy set at 150mm long that reaches into a recessed wheel without marking it. Reading what the set actually contains is more useful than the piece count printed on the case.
Diesel work has its own sets because the fittings are unusual. Glow plug sets run extra long at 35mm and thin wall PSG at 18 pieces, and Bosch injector pump, injection line and EGT sensor sets cover fittings no general socket reaches. E-Type and external Torx Plus sets cover splined heads. Questions go over WhatsApp on 07754288583. Thin wall PSG and extra long forms exist because the plug well leaves no room for a standard socket.