Thrumming is fun! In just a couple of days, I knit this hat.
Using some left over Briggs & Little yarn at 18 stitches to four inches and some left over B&L roving, I cast on 112 stitches. In retrospect that was a few too many. 96 would have given me a closer fitting band. The 112 came from some ravelry research where knitters knit their thrummed hats using knitting worsted yarn, at 20 stitches to four inches. I knew my yarn was a bit thicker BUT to increase wind resistance and keep the thrums from getting loose I decided to use smaller-than-normal needles and chose 3.75mm. With that smaller needle, I thought I needed the extra stitches to compensate. Turns out I didn't. The hat won't blow off but could have benefitted from a tighter band.
There are four and a half inches of 2x2 ribbing - enough to fold double over the ears. Three rows of plain knitting follow the ribbing before beginning the thrummed rows. Thrummed rows are
three rows apart. For no particular reason, I chose to offset the thrums. The first off-set row required concentration but after that it was simple to follow the pattern.
Knitting for an average adult, I knit the hat to a depth of five and a half inches from the bottom of the folded ribbing before beginning the decreases. My hats and my socks have decrease rounds in common. I prefer the 'rounded' look. To accomplish this, I decrease every other round until half the stitches have disappeared, then decrease every round. That faster rate of decrease keeps the hat a bit flatter, less pointy, on top.