This is the Three-Cornered Hat found in Elizabeth Zimmermann’s Knitter’s Almanac for the month of “June”, which also features the Ganomy Hat and the Maltese Fisherman’s Hat.

Elizabeth Zimmermann’s description for the Three-Cornered Hat:

“Why must a Tam-o’-Shanter be round? Can’t it be octagonal, pentagonal, square or triangular? I’ve not tried out the first three, but I’ve made a Three-Cornered Hat, and it finds favor with all who try it on. Wear it down or up, with the point to the front or the back, or with all points tucked in--it has as many lives as a cat.”