Overhand, Overhand Stopper Knot

A very easy to tie stopper is essentially two overhand knots

Make a bight and tie first overhand knot

Bring left hand strand over the bight

Bring right hand strand under the bight

Bring the uppermost strand down through the right hand bight

And bring other strand up through its bight

Bring the right hand strand up through the small bight of the first overhand knot

And bring the left hand strand down through the other bight

Grab the loop in one hand and the two strands in the other hand and pull apart. Adjust to tighten