With a little thought about the cam it is often possible to set a 100% secure cam in a crack that only takes 75% of the width of the cam, and in some cases a 100% unit where it seems half the cam is hanging out of the crack!
The most important thing to remember is that a cam has two ordinations, a wide ordination and a narrow one, and that if a cam is unstable and weak one way, may be solid if you flip it over (this is most noticeable in a Tricam or 3CU). Imagine a cam working like a triangle, with the force coming from the outside cams being the base, and the two central cams the point. Very often a shallow crack in a corner will have a broad face on one side and a shallow one on the other. Place the cam with the wide cams on the broad face and the central cams touching the shallow side. If the crack is very shallow you may find that one of the central cams is not touching at all. don’t be alarmed, it may not be 100% but the strength of 3 cams should still be effective (the cam is working like TCU).
As you can imagine, the narrower the cam (Aliens, Totems), the greater the opportunity for all cams engaging the rock, or being able to provide affective protection on the shallowest of cracks.
The Totem has another advantage in that it can clipped off onto two cams which although not as strong as 3 or 4, could still be effective.
Andrew Kirkpatrick is a British mountaineer, author, motivational speaker and monologist. He is best known as a big wall climber, having scaled Yosemite's El Capitan 30+ times, including five solo ascents, and two one day ascents, as well as climbing in Patagonia, Africa, Alaska, Antarctica and the Alps.Follow @ Instagram