I have a leak in my single handle bathroom faucet. I can't find any stamp or marking on it to indicate the manufacturer. Turning off the hot water fixes the problem short term. I have found some great online tutorials for repairing all potential types of these sinks, but I can't get the handle off to even begin to work on it. We have several Allen wrenches but none fit. It does not appear to be a typical screw, or maybe it is not a screw at all? It looks like a post that is threaded around the outside with a perfectly round hole in the center that is not threaded. The faucet is only five years old and I don't want to replace the whole thing if it can be avoided.
The bright spot in the middle is a post that seems to prevent inserting an allen wrench.