IMPs (Immaculate Marginal Protection) are 'brass' micro wires that have a regular taper and are very similar, if not identical, to the famous RPs. The heads are machined on a from a copper alloy that has very specific properties and a carefully controlled hardness to allow both good bite and also a good resistance to shear forces - this way the nuts lock into the rock well and also resists being pulled through the placement. The heads are silver soldered onto stainless steel wire and every unit is proof loaded to 75% of its rated strength.
The colour coded alloy swage is only crimped on one side so that one wire runs freely in order that the head is always loaded optimally when it holds a fall.
There is no size 0: DMM suggest using a Brass Offset 0 if you need a wire this small.