I have see washers with a square hole in them and four prongs on one
side. These washers fit on the square part of a carriage bolt and when
the two pieces of wood are drawn together the four prongs bit into the
wood and prevent the carriage from turning. These washers are ideal if
the carriage bolt is ever to be removed. I have seen these washers
used on wooden play structures. Does anybody know what these washers
are called and where they may be purchased. Thanks in advance for all
answers.

Vic