This has a long tube with securing nut on the inside, so this can be firmly held in place.
If this is well-sealed with a good quality sealant, this will significantly reduce the possibility of water getting into the transom and causing degradation.
Round external flange, with guide marks to show that the plug is properly tightened.
Dimensions
Diameter of outer flange: 43mm
Drill diameter required: 27mm
Maximum thickness of transom: 80mm
Diameter of inner nut: 41mm (across corners)
Internal diameter: 19mm
Bung type: screw-in with o-ring seal, with retainer