Looks like a thermowell. Got any temperature instrumentation that suddenly went dark? Snarky comment, the only way that could be in a strainer is if it was inside the piping, whereas in normal use the part is threaded into a pipe tap or weldolet on the side of the pipe. Probably was there when the piping was bolted up, and slowly drifted downstream. This is why you have strainers, be thankful. We are a valve company, and the stuff we have found lodged in returned valves is stunning. Weld slag and wire, pipe fittings, bolts and nuts, washers - I can understand. But ladies undergarments?