These are brand new solid brass sump plugs for all Cloud, Shadow and Spirit oil sumps.  They also fit the final drive drain and the fuel tank drain for Shadows and Spirits - and anything else that takes UG526.  They also fit the sumps on the Austin Princess Vanden Plas equipped with the RR FB60 engine.  This is also appropriate to replace RG3744 on EPW cars.  These feature a flange that is slightly thicker than stock to better resist deforming.  The internal hex is slightly deeper too to allow for better tool engagement.  The internal hex is the stock size of .525" - the same as the multi-tool in your tool kit.  Missing your multi-tool?  BTW also offers reproduction multi-tools and 1/2" drive sockets that are accurately machined to precisely fit these plugs with no slop.  These items are available under the "Tools" tab.
New laser cut sealing washers made from dead soft 1100 aluminum are available as well.  Get a bunch of them because they're cheap and never feel tempted to re-use an old one again.