IMPs let you take advantage of the smallest and most marginal placements. Nut heads are made of brass, allowing them to bite into small placements but making them strong enough to resist pulling through. These are soldered directly on to wires, allowing a thicker wire to be used and increasing the strength of the IMP. The swage on the wire is colour coded for quick size selection, and allows one side of the wire to slide, letting the IMP self equalize when loaded and increasing placement security. IMP's are invaluable for those pushing into harder grades and needing to take advantage of all protection options.