For the american lock keyway, I find that the usual tensors are not wide enough to work without causeing some problems from slipping, go to the local mechanics and get him to let you take all the windshieldwipers out of his trash, there should be a variety. the longer ones will have thicker stainless stiffeners, take all the wiper stiffeners you can get. they will all be good for some project.
chose one of the wider ones, and make a tensor that is only about half an inch long in the blade, use a file to knock off the sharp edges which you don't want biting into the cylinder wall or the pick moving above it. the reason you don't want the tensor to go in very far is to leave room for the pick to manouver under the deeper pins. a fairly broad tensor works well with american, and the lengh of the tensor handle should not be longer than your finger, the longer it is, the more leverage it has and this binds the pins tight, you are looking for something you can sense so piling on the leverage is not helpful.
for everone whos tensors have handles longer than your finger, do this, pinch the tensor between thumb and forefinger and be determined that you will pinch it so hard that it wont turn, then use a feather or a piece of paper to push on the far end of that tensor.
