Standard Gauge with Ribber
30gr sock yarn (I used old Kroy 4ply, which lists a stockinette gauge of 28st/4")
waste yarn in a highly contrasting colour
Cast on every other needle: MB 30L-31R; RB 29L-30R; do the zig zag row and hang weights, and then the "circular" or "tubular" cast on at T3 (or even a little tighter).
Switch to 1x1 rib and T4. RC=000. Rib for 20 rows.
Now to increase for the thumb gusset. Move the outer stitch at each edge, on both beds, out one position (keep every other needle out of work). Take the heel of the st towards the center of the bed, and place it on the empty needle (so, don't take the heel of the outer stitch that was moved, but from the first st beside it).
Knit four rows.
Repeat these two steps; making increases when RC reads 20, 24, 28, 32, 36. That makes 10 sts increased at either edge. When RC=40, take the 10 sts at each end off onto waste yarn threaded through each stitch (one strand for the MB sts, one strand for the RB sts is fine). Knot the strands!
Continue ribbing till RC=64. This makes a long hand that can be folded back for better finger exposure, or left long to keep fingers warm. Remove main yarn and thread up waste yarn. Set the carriage to knit circular, and knit about 20 rows (10 rounds).
Now, the hard part, which isn't all that hard, you just have to visualize. So far, there is a seam going up the thumb side of the hand, right up to where the sts have been taken off. We will re-hang those sts to keep ribbing, and keep the seam on the outer thumb, but the thumb will be knit in one piece. Start hanging the left side of the thumb (anywhere on the beds), (make sure to hang the original MB sts on the MB...I'm sure most of you would know this, but ahem..some of us need reminders). The 10st is on the RB. Bring the next MB needle in pattern into work, then the RB needle, then another MB needle. These three needles will be empty. Continue hanging the other half of the thumb, starting from the inner part which should be a RB stitch.
Make sure carriage is set to rib, T4, RC=000. Take carriage across, and you can see those empty 3 needles in the middle should now have yarn across them. You can hang a "7" hanger and light weight, or just knit the next row slowly and make sure those sts knit properly, add a claw weight when you can. Rib for 10 rows. Switch to waste yarn and set the carriage to circular, and knit 10 rounds/20 rows. Take it off the machine, cutting the main yarn with a long tail.
It now looks like this, if you fold it to make it look like a glove:
But look closely at that weird thumb:
Here, you can see, sort of, how the outer stitches that were increased, are pulled around and joined in the middle, not joined by the outer edges. If that step was too confusing, feel free to just rib those 10 st on each side separately (and infact, this might make them a smidge quicker as you could leave the hand in hold position while you do each side of the thumb, but it would mean two seams, and you'd have to add one (or more) stitch where the thumb meets the body)To finish off the top, and the thumb, I used the "Smiles and Frowns" cast off from Diana Sullivan's Ribber Course videos. If you haven't seen those, you should, they are awesome. Ribbing is very stretchy so if you want to make them for an adult, I'd try casting on only a bit more, MB 32-33, RB 31-32....keep the MB as the outer sts. The gloves I made for an adult took 50gr, just for reference. 30gr is what I seem to always have left over from a 100gr ball of sock yarn. Diana's adult tam takes 50gr, so you should be able to get a pair of gloves or wrist warmers and a tam from one 100gr ball!