Angela Sixian Wu designed three adorable tams. My version of her Tam C is pictured above. These are free internet patterns available from knitty archives. I've made two of the tams and love them - definitely one of my favorite hats! Because you use a self-striping contrast color yarn, it's a really easy "fair isle" look.
Brim Circumference (unstretched, before blocking): 18 inches
Tam Circumference (unstretched, before blocking): 24 inches
After blocking with a 10.5 inch diameter plate, the finished tam will have a circumference of 33 inches (10.5 inches in diameter).
Worsted weight yarn - 1 skein (I used Blue Sky Suri Merino)
Noro Silk Garden yarn - 1 skein
RECOMMENDED NEEDLE SIZE:
(1) 16-inch US#4/3.5mm circular needle
(1) 24-inch US#6/4mm circular needle
US#6/4mm double-point needles
(Always use a needle size to give the gauge listed)
S2KP: Slip next 2 sts together knitwise, as if working a k2tog; k next st, pass slipped sts over. Forms a centered double decrease.
Corrugated Rib (Worked in the round over an even number of sts):
Set-up Round: [K1 using MC, k1 using CC] to end.
Pattern Round: [K1 using MC, p1 using CC] to end.
Repeat Pattern Round for Corrugated Rib
Place marker and join to begin working in the round, being careful not to twist.
Work 7 rounds in Corrugated Rib.
Next Round: Using MC, [k4, m1] to end.
Switch to 24-inch
Except where otherwise noted, chart is worked 6 times in each round.
When last round of chart is complete, 6 sts remain. Break yarn.
Draw tail through remaining sts and pull tight.
The decreases are a bit tricky....the decrease is a centered double decrease. You need to slip two stitches to the working needle as if you were going to knit them together (insert from the side of the second stitch), then knit the next (third) stitch and pass the two slipped stitches over the knitted one. Before you do this maneuver, you need to slip the last stitch of the previous row over before you knit it; the previous row is one stitch shorter than it would otherwise be. It's helpful to identify the exact stitch that needs to be on top for the decrease and ensure that it's that stitch that you insert the needle through when you slip two as if to k2tog. Rearrange the stitches as the row juncture to make it happen.
Soak tam in water with a small amount of a gentle soap. Rinse, and squeeze gently to remove excess water.
Stretch tam over 10 1/2" dinner plate, positioning the tam carefully so that the pattern is centered. Allow to dry completely.
*** I find the 10 1/2" dinner plate is a wee bit large. I'd go 9 1/2" to 10".