The Oysterman's Stopper Knot, or Ashley's Stopper Knot, is simple to tie, it is strong and bulky, and has a handsome threefold symmetry when looked from the underside. This knot creates a flat triangular shape that is thicker than most other knob knots.
To Tie an Oysterman's Stopper Knot:
Tie a Slip Noose, making a tuck through the loop.
Tuck the working end through the noose.
Pull the standing part to trap the running end with the loop.
As you tighten the knot, you should get the finished Oysterman's Stopper.