Metric Countersunk Sealed Plug

For an M26 x 1.5 metric threaded port, the fit matches since the plug has a male M26 x 1.5 thread. It is made for closing off unused metric threaded ports in hydraulic circuits.

that's correct. This countersunk plug has a male M26 x 1.5 metric thread, so it'll fit your M26 x 1.5 port as long as it's a standard metric thread.

Male M26 x 1.5 is the thread on this one. The countersunk profile is what makes it sit flush or even slightly recessed into the port face rather than protruding outward. That low-profile fit is really the whole point of the countersunk design, keeps things clean where clearance is tight or where a protruding plug would get in the way.