Never buy an adjustable stem for a bicycle; that bit of advice sent me from pillar to post today until I'd fixed that mistake. Two bike shops, a Canadian Tire*, and home at last, late and tired. The reason: the adjustable stem I'd bought just last month had started to get wobbly, and the response I got from the pro in the first shop was, "Never buy those. We don't even sell them." When I got to the second store, the fellow said, "A new stem? Sure, but we don't sell adjustable stems."
*Amazingly, I found someone at the Canadian Tire who was really helpful. Or rather, he found me, stopping to ask if he could help, and then proving that he could, in abundance.