Review on 🔌 Pack of 4 Inverted Flare Steel Plugs for 3/8"-24 – Available at The Stop Shop by Dave Butler

The larger 9/16 x 18 plug I tried on the GM master cylinder leaked right away. The plug is tapered, but the center is not deep enough to properly fit into the cone of most master cylinders. As others have pointed out, the larger forks don't have a hex head. They are hexagonal heads. Luckily I had an old set of connectors that I used for this project. I would look elsewhere if you want something that actually works.